Hysteretic current mode buck-boost control architecture

ABSTRACT

A hysteretic current mode buck-boost voltage regulator including a buck-boost voltage converter, a switching controller, a window circuit, a ramp circuit, and a timing circuit. The timing circuit may be additional ramp circuits. The voltage converter is toggled between first and second switching states during a boost mode, is toggled between third and fourth switching states during a buck mode, and is sequentially cycled through each switching state during a buck-boost mode. The ramp circuit develops a ramp voltage that simulates current through the voltage converter, and switching is determined using the ramp voltage compared with window voltages provided by the window circuit. The window voltages establish frequency, and may be adjusted based on the input and output voltages. The timing circuit provides timing indications during the buck-boost mode to ensure that the second and fourth switching states have approximately the same duration to provide symmetry of the ramp signal.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application Ser.No. 62/062,463, filed on Oct. 10, 2014, which is hereby incorporated byreference in its entirety for all intents and purposes.

BRIEF DESCRIPTION OF THE DRAWINGS

The benefits, features, and advantages of the present invention willbecome better understood with regard to the following description andaccompanying drawings, in which:

FIG. 1 is a simplified block diagram of an electronic device configuredwith a power system including a voltage regulator implemented accordingto an embodiment of the present invention;

FIG. 2 is a simplified schematic and block diagram of the voltageregulator of FIG. 1 according to one embodiment of the presentinvention;

FIG. 3 is a tabular diagram illustrating multiple operating orregulation modes and the corresponding switching states S0-S3 of thebuck-boost charger controller of FIG. 2 for controlling operation of thevoltage regulator of FIG. 1 in either buck or boost regulation mode andfor regulating or otherwise maintaining a voltage level of the outputvoltage according to one embodiment of the present invention;

FIG. 4 is a simplified schematic diagram of a current mode controlmodulator according to one embodiment of the present invention that maybe incorporated within the buck-boost charger controller of FIG. 2;

FIG. 5 is a timing diagram illustrating a desired waveform for a rampvoltage VR1 according to one embodiment of the present invention; and

FIGS. 6-14 are timing diagrams of nine different configurations of themodulator of FIG. 4 for generating the desired waveform of the rampvoltage VR1 shown in FIG. 5 during the buck, boost and buck-boostregulation modes.

DETAILED DESCRIPTION

Voltage regulators that convert an input voltage to a regulated outputvoltage operate in buck mode when the input voltage is greater than theoutput voltage, and operate in boost mode when the input voltage is lessthan the output voltage. When the input voltage ranges from less than togreater than the output voltage, the voltage regulator must support bothmodes and must switch between the modes. Also, a buck-boost mode may besupported when the input and output voltages are sufficiently close toeach other. Conventional voltage regulators have significant modetransition regulation problems between buck and boost modes. Traditionalmethods used fixed clock systems and added patches to help smooth themode transitions which often added complexity and which can sacrificesystem speed, linearity, and transient response. Hysteretic current modecontrol architectures provide the fastest transient response in buck andboost modes and do not require slope compensation, but also havesignificant regulation challenges near the buck-boost boundary, that is,when the input and output voltages are near to each other.

A hysteretic current mode buck-boost control architecture as describedherein improves mode transitions between buck, buck-boost, and boostregulation modes, and further improves load transient response.

FIG. 1 is a simplified block diagram of an electronic device 100configured with a power system 101 including a voltage regulator 103implemented according to an embodiment of the present invention. Thepower system 101 develops one or more supply voltages which providepower to other system devices of the electronic device 100. In theillustrated embodiment, the electronic device 100 includes a processor107 and a peripheral system 109, both coupled to receive supply voltagesfrom the power system 101 via a supply bus 105, which includes anycombination of power and/or signal conductors. In the illustratedembodiment, the peripheral system 109 may include any combination of asystem memory 111, such as any combination of random-access memory (RAM)and/or read-only memory (ROM) type devices and memory controllers andthe like, and an input/output (I/O) system 113, which may include systemand peripheral controllers and the like, such as graphic controllers,interrupt controllers, keyboard and mouse controllers, system storagedevice controllers (e.g., controllers for hard disk drives and thelike), etc. The illustrated system is exemplary only, since many of theprocessor system and support devices may be integrated onto theprocessor chip as understood by those skilled in the art.

The electronic device 100 may be any type of computer or computingdevice, such as a computer system (e.g., notebook computer, desktopcomputer, netbook computer, etc.), a media tablet device (e.g., iPad byApple Inc., Kindle by Amazon.com, Inc., etc.), a communication device(e.g., cellular phone, smartphone, etc.), among other types ofelectronic devices (e.g., media player, recording device, etc.). Theelectronic device 100 may operate with a battery, which may or not beremovable and which may or may not be rechargeable. In many suchconfigurations, the battery is rechargeable (e.g., rechargeable battery219, FIG. 2) and a separate alternating current (AC) adapter is provided(e.g., adapter 201, FIG. 2) to provide power to the electronic device100 and/or recharge the battery.

FIG. 2 is a simplified schematic and block diagram of the voltageregulator 103 according to one embodiment of the present invention. Anadapter 201 is coupled between and adapter node 202 and a reference node(shown as ground or GND), so that the adapter node 202 develops anadapter voltage VAD when connected to the electronic device 100. A senseresistor 203 with resistance RS1 is coupled between node 202 and aninput node 204 developing an input voltage VIN. An input capacitor 205with capacitance CI is coupled between the input node 204 and GND. Abuck switching stage 207 is coupled between the input node 204 and GND.The buck switching stage 207 includes a first transistor Q1 havingcurrent terminals coupled between the input node 204 and a firstintermediate node 206, and a second transistor Q2 having currentterminals coupled between node 206 and GND. An output inductor 209 withinductance LO is coupled between the first intermediate node 206 and asecond intermediate node 208. A boost switching stage 211 is coupledbetween an output node 210 developing an output voltage VOUT and GND.The boost switching stage 211 includes a first transistor Q4 havingcurrent terminals coupled between the output node 210 and the secondintermediate node 208, and a second transistor Q3 having currentterminals coupled between node 208 and GND. The buck and boost switchingstages 207 and 211 collectively form a buck-boost switching stage.

An output capacitor 213 with capacitance CO and a system load 215drawing system current ISYS (or load current) are both coupled betweenthe output node 210 and GND. The system load 215 represents anycombination of the system devices drawing load current, such as theprocessor 107, the system memory 111, the peripheral system 109, etc. Asecond current sense resistor 217 with resistance RS2 is coupled betweenthe output node 210 and a node 212, which is coupled to one currentterminal of a transistor Q5. The other current terminal of Q5 is coupledto a battery terminal 214 developing a battery voltage VBAT, which isfurther coupled to a positive terminal of a rechargeable battery 219.The rechargeable battery 219 has a negative terminal coupled to GND. Abuck-boost charger controller 221 is provided for controlling operationas further described herein.

The transistors Q1-Q5 are each shown as MOS or FET type transistors,such as a P-type MOS (PMOS) or P-type FET (PFET) transistor, an N-typeMOS (NMOS) or P-type FET (PFET) transistor, or a MOSFET transistor orthe like. Alternative power switching devices or electronic controlswitches are contemplated, such as bipolar junction transistors (BJTs)and the like, insulated-gate bipolar transistors (IGBTs) and the like,etc. Each transistor device is sized and configured to perform theintended function.

The buck-boost charger controller 221 has inputs coupled to nodes 202and 204 for sensing the voltage across the sense resistor 203, hasanother input coupled to the input node 204 for sensing the inputvoltage VIN, has inputs coupled to nodes 210 and 212 for sensing thevoltage across the sense resistor 217, has an input coupled to theoutput node 210 for sensing the output voltage VOUT, and has outputsQ1G, Q2G, Q3G, Q4G and Q5G coupled to control terminals (e.g., gateterminals) of transistors Q1, Q2, Q3, Q4 and Q5, respectively. Thebuck-boost charger controller 221 senses adapter current (provided bythe adapter 201) via the voltage across the sense resistor 203, andsenses battery current (charge or discharge current) through the battery219 via the voltage across the sense resistor 217. The buck-boostcharger controller 221 controls buck and boost operation as describedherein by controlling the transistors Q1-Q4 via the Q1G-Q4G signals,respectively. The buck-boost charger controller 221 controls batterycharge/discharge by controlling the transistor Q5 via the Q5G signal.The buck-boost charger controller 221 is configured as a battery chargesystem or the like for detecting the adapter 201 and the battery 219,for charging and/or discharging the battery 219, and for controlling thesource of power for providing the system current ISYS to the load.

The buck-boost charger controller 221 operates according to pulse widthmodulation (PWM) for controlling switching of the transistors Q1-Q4. Asdescribed further herein, however, the switching states of the systemdepend upon the regulation mode and the relative voltage levels of theinput and output voltages. In normal buck or boost configurations, asingular PWM signal with two states may be used to control switchingoperation. The buck-boost charger controller 221, however, operates infour switching states for controlling switching in separate buck, boostand buck-boost regulation modes, so that PWM operation is defined usingfour separate switching states S0, S1, S2 and S3 as further describedherein.

The voltage regulator 103 is configured as a hysteretic current modebuck-boost control system as further described herein. Although thevoltage regulator 103 is configured as a battery charge system, any typeof configuration or system is contemplated in which a voltage regulatoris employed. The buck switching stage 207, the boost switching stage 211(collectively, the buck-boost switching stage) and the output inductor209 of the voltage regulator 103 collectively form a buck-boost voltageconverter 223 that converts the input voltage VIN to the regulatedoutput voltage VOUT under control of the buck-boost charger controller221. In one embodiment, the voltage regulator 103 is configured toregulate any one of multiple parameters, such as input voltage VIN,output voltage VOUT, input current (such as detected through the adapter201), battery current through the battery 219, etc. Although not furtherdescribed, the voltage regulator 103 may be configured to switch betweenmultiple parameters to control one parameter at a time based onoperating and system conditions.

FIG. 3 is a tabular diagram illustrating multiple switching states S0-S3of the buck-boost charger controller 221 for controlling operation ofthe voltage regulator 103 in each of the buck, buck-boost and boostregulation modes and for regulating or otherwise maintaining a voltagelevel of VOUT according to one embodiment of the present invention. Theactivation states of the particular transistors depends upon theswitching state, and the transitions between the switching statesdepends upon the particular regulation mode. In the illustratedembodiment, each gate control signal QXG is pulled high to turn on acorresponding transistor QX, and pulled low to turn off the transistor,in which “X” any one of the transistors 1-4. For example, Q1G is pulledhigh to turn Q1 on, and pulled low to turn Q1 off.

A first switching state S0 (Boost On) occurs when Q1 and Q3 are turnedon (Q1G and Q3G high) and Q2 and Q4 are turned off (Q2G and Q4G low). Instate S0, one end of the output inductor 209 is coupled to VIN and theother to GND, so that the inductor voltage is VIN. A second switchingstate S1 (Boost Off) occurs when Q1 and Q4 are turned on and Q2 and Q3are turned off (Q3G pulled low and Q4G pulled high). In state S1, oneend of the output inductor 209 is coupled to VIN and the other end toVOUT, so that the inductor voltage is VIN−VOUT. A third switching state(Buck Off) occurs when Q2 and Q4 are turned on and Q1 and Q3 are turnedoff. In state S2, one end of the output inductor 209 is coupled to GNDand the other end to VOUT, so that the inductor voltage is −VOUT. Afourth switching state (Buck On) occurs when transistors Q1 and Q4 areturned on and Q2 and Q3 are turned off. In state S3, one end of theoutput inductor 209 is coupled to VIN and the other end to VOUT, so thatthe inductor voltage is VIN-VOUT.

In the boost regulation mode, Q1 is on and Q2 is off, and operation iscontrolled by switching between Q3 and Q4. In the buck regulation mode,Q3 is off and Q4 is on, and operation is controlled by switching betweenQ1 and Q2. In the buck-boost regulation mode, operation switches betweenup to all of the switching states S0-S3 as further described herein. Theswitching states S0-S3 generally control the gate drive signals Q1G-Q4Gfor controlling the activation states of the transistors Q1-Q4,respectively.

FIG. 4 is a simplified schematic diagram of a current mode controlmodulator 400 according to one embodiment of the present invention. Themodulator 400 includes combined control signals which may be used withinthe buck-boost charger controller 221 for generating the gate controlsignals Q1G-Q4G for controlling operation of the voltage regulator 103.The modulator 400 includes a primary ramp circuit 428 for developing aprimary ramp signal VR1. The modulator 400 may further include a timingcircuit that is used to ensure that the durations of TS1 and TS3 areapproximately equal. In one embodiment, the timing circuit includesadditional ramp circuits 430 and/or 450 as further described herein.

The ramp circuit 428 includes a current source 401 providing a currentII is coupled between a source voltage, shown as VDD, and one switchedterminal of a switch 403. The switch 403 is shown as a single-pole,single-throw (SPST) type switch having its other switched terminalcoupled to a ramp node 402 developing the ramp voltage VR1. Another SPSTswitch 404 has one switched terminal coupled to the ramp node 402 andits other switched terminal coupled to another current source 405. Thecurrent source 405 develops a current IO and is coupled between theswitch 404 and GND. The current II developed by the current source 401is proportional to a transconductance gain GM multiplied by the inputvoltage VIN, or II∝GM*VIN, and the current IO developed by the currentsource 405 is proportional to the transconductance gain GM multiplied bythe output voltage VOUT, or IO∝GM*VOUT. As shown, when switch 403 isclosed, the current source 401 sources current II to the ramp node 402,and when switch 404 is closed, the current source 405 draws or sinkscurrent from the ramp node 402. Proportional relationships describedherein are intended to mean that an additional gain factor may beincorporated, although the gain factor may be “1” or “−1”. For example,the current II may instead be represented as IO=K*GM*VOUT.

A transconductance amplifier or the like (not shown) withtransconductance gain GM may be used to implement each of the currentsources 401 and 405. For example, a first transconductance amplifierreceiving VIN may implement the current source 401, and anothertransconductance amplifier receiving VOUT may implement the currentsource 405. The switches 403 and 404 may be implemented in any suitablemanner, such as at least one electronic switching transistor (e.g., FETor MOS transistor or the like). The switch 403 has a control inputreceiving a control signal CTRL1, and the switch 404 has a control inputreceiving another control signal CTRL2. In each case, when the controlsignal is asserted to a first logical state, such as being assertedhigh, then the switch is closed, and when asserted to a second logicalstate, such as being asserted low, then the switch is opened.

A ramp capacitor 407 with capacitance CR1 is coupled between the rampnode 402 and GND, and a resistor 409 with ramp resistance RR is coupledbetween the ramp node 402 and a reference or bias voltage VREF. The rampnode 402 is provided to the positive (or non-inverting) input of acomparator 411, to the negative (or inverting) input of a secondcomparator 413, and to the positive input of a third comparator 425. Thecomparator 411 asserts a control signal C1, the comparator 413 asserts acontrol signal C2, and the comparator C3 asserts a control signal C3,each provided to a switching controller 415.

An error amplifier 417 generally amplifies the difference between acontrolled parameter of the voltage regulator 103 and a target orreference voltage and develops a compensation or control voltage VC. Inone embodiment, for example, the output voltage VOUT, or a sensedversion thereof, along with an output reference voltage (not shown) areprovided to the error amplifier 417 for developing VC. Additional loopcompensation circuitry (not shown) may be provided.

The control voltage VC is provided to a negative terminal of a voltagesource 419 developing an upper voltage VP1, having its positive terminaldeveloping a positive window voltage VWP provided to the negative inputof the comparator 411. VC is also provided to a positive terminal ofanother voltage source 421 developing a lower voltage VN1, having itsnegative terminal developing a negative window voltage VWN provided tothe positive input of the comparator 413. The control voltage VC variesbased on operating conditions in order to control the regulatedparameter. Regardless of changes of VC, the voltage VWP remains above VCby the upper voltage VP1 and the voltage VWN remains below VC by thelower voltage VN1. In other words, VWP and VWN both follow VC at therespective offset voltages above and below VC. The difference betweenVWP and VWN is a window voltage VWIN, or VWIN=VWP−VWN.

The switching controller 415 receives the control signals C1, C2 and C3,along with other control signals C4, C5, C6, C7 and C8, describedfurther below, controls the control signals CTRL1-CTRL10, and determinesthe switching states S0-S3 of the voltage regulator 103. The switchingcontroller 415 generates the gate drive signals Q1G-Q4G based on thedetermined switching state to turn on and off the transistors Q1-Q4 asshown in FIG. 3. In an alternative embodiment, the switching controller415 may provide switching state signals (not shown) to a separate drivecontroller (not shown) which converts the indicated switching states tothe gate drive signals Q1G-Q4G for controlling operation of thetransistors Q1-Q4.

In one embodiment, the ramp circuit 428 of the modulator 400 operatesaccording to a synthetic ripple configuration, in which the ramp voltageVR1 replicates or synthetically simulates the ripple current through theoutput inductor 209. In the buck regulation mode of operation, operationtoggles between states S2 and S3 in which Q3G is low to keep Q3 off, Q4Gis high to keep Q4 on, and Q1G and Q2G are each toggled to oppositestates with respect to each other to toggle activation of Q1 and Q2. Inthis manner, the output end of the output inductor 209 remains coupledto VOUT, and the input end is switched between the input voltage VIN andGND, CTRL2 remains asserted to keep switch 404 closed, and CTRL1 istoggled high and low to control switching operation by turning switch403 on and off.

When CTRL1 is high, the switch 403 is closed in which the current source401 charges the capacitor 407 with a current proportional to the inputvoltage while the current source 405 discharges the capacitor 407 with acurrent proportional to the output voltage. In the buck mode sinceVIN>VOUT, the ramp voltage VR1 ramps up replicating the current throughthe output inductor 209 proportional to VIN−VOUT consistent with theswitching state S2. When CTRL1 is low, the switch 403 is opened in whichonly the current source 405 discharges the capacitor 407 with a currentproportional to the output voltage. In this case, the ramp voltage VR1ramps down replicating the current through the output inductor 209 whenits voltage is VOUT (or −VOUT since VR1 ramps down as the ramp capacitorCR1 discharges) consistent with the switching state S3.

In the boost regulation mode of operation, operation toggles betweenstates S0 and S1 in which Q2G is low to keep Q2 off, Q1G is high to keepQ1 on, and Q3G and Q4G are each toggled to opposite states with respectto each other to toggle activation of Q3 and Q4. In this manner, theinput end of the output inductor 209 remains coupled to VIN, and theoutput end is switched between the output voltage VOUT and GND, CTRL1remains asserted to keep switch 403 closed, and CTRL2 is toggled highand low to control switching operation by turning switch 404 on and off.

When CTRL2 is low in the boost mode, the switch 404 is opened in whichthe current source 401 charges the capacitor 407 with a currentproportional to the input voltage VIN. The ramp voltage VR1 ramps upreplicating the current through the output inductor 209 when its voltageis VIN since VR1 ramps up as the ramp capacitor CR1 charges consistentwith the switching state S0. When CTRL2 is high, the switch 404 isclosed in which the current source 401 continues to charge the capacitor407 with a current proportional to the input voltage while the currentsource 405 discharges the capacitor 407 with a current proportional tothe output voltage. In the boost mode since VOUT>VIN, the ramp voltageVR1 ramps down replicating the current through the output inductor 209proportional to VIN−VOUT consistent with the switching state S1. In theboost regulation mode, VR1 ramps up and down between the voltages VWPand VWN.

The voltage sources 419 and 421 and the comparators 411 and 413 form ahysteretic comparator. During both the buck and boost regulation modes,the switching controller 415 monitors the control signals C1 and C2 andasserts the control signals CTRL1 and CTRL2 and the gate drive signalsQ1G-Q4G accordingly in which VR1 ramps up and down within the windowvoltage VWIN between VWP and VWN. As further described herein, abuck-boost regulation mode is defined in addition to the buck and boostregulation modes, and facilitates transitioning from buck to boost orfrom boost to buck as the voltage level of VIN varies relative to VOUT.Additional circuitry is used to implement the buck-boost regulationmode. Also, VR1 is configured to ramp outside the nominal voltage windowVWIN as further described herein.

In any of the regulation modes, the voltage regulator 103 employshysteretic current mode control in which the switching frequency isvariable and changes based on load conditions. Although the actualswitching frequency FSW is allowed to vary in response to loadconditions, the switching frequency may be controlled towards a targetsteady state frequency level FSS. In one embodiment, the steady statefrequency level FSS is 1 Megahertz (MHz), although any suitableswitching frequency is contemplated. The switching frequency FSW may becontrolled based on any one of several different methods. In oneembodiment as further described herein, FSS is determined and maintainedin an open loop method based on the voltage levels of VIN and VOUT. Inanother embodiment, FSW is measured, such as by measuring the frequencyof the operative switching signals in any given regulation mode (usingtimers or counters or the like), and the measured frequency is comparedwith the target frequency FSS and operation is adjusted accordingly.

The switching frequency may be adjusted based on any suitable method. Inone embodiment, the upper and lower voltages VWP and VWN are bothadjusted so that VWIN is adjusted to adjust the switching frequency FSWback towards the target steady state frequency level FSS. For example,to increase frequency, VWP and VWN may both be temporarily reduced bythe same amount, and to decrease frequency, VWP and VWN may both betemporarily increased by the same amount. In this manner, the actualswitching frequency FSW may change temporarily to quickly respond toload transients, but settles quickly back to the steady state switchingfrequency FSS when the load condition is stable.

In one embodiment, a frequency controller 406 is provided, such aswithin the switching controller 415, that controls the voltage sources419 and 421 to adjust the voltages VWP and VWN to adjust the windowvoltage based on the voltage levels of VIN and VOUT to maintain thesteady state frequency FSS. In the buck regulation mode,VWIN∝PER*(VIN−VOUT)*VOUT/VIN, where “PER” is the target period of FSS.For example, if FSS=1 MHz, PER=1 microsecond (μs). In the boostregulation mode, VWIN∝PER*(VOUT−VIN)*VIN/VOUT. In the buck-boostregulation mode when VIN>VOUT, VWIN∝PER*VIN*VOUT/(3*VIN+VOUT). In thebuck-boost regulation mode when VOUT>VIN,VWIN∝PER*VIN*VOUT/(3*VOUT+VIN). In each expression, a gain factor “K”may be used to replace proportionality with equality, in which “K” mayinclude 1 or −1. The switching controller 415 may further ensure aminimum period for each of the switching states. In one embodiment, atimer may be provided that is initiated for each switching statetransition and prevents the next transition from occurring until thetimer times out indicating the minimum switching period time. In anotherembodiment, the frequency controller 406 simply prevents the voltagesVP1 and VN1 from falling below a predetermined minimum level indicativeof the minimum switching period time.

The modulator 400 includes a timing circuit for meeting timingconditions as further described herein. In the illustrated embodiment,the timing circuit comprises at least one additional ramp circuit, shownas the ramp circuit 430, for developing a second ramp signal VR2. Asfurther described herein, VR2 may be used as a timing ramp signal forcontrolling the duration of one or both switching states S1 and S3during the buck-boost regulation mode. The ramp circuit 430 isconfigured in a similar manner as the primary ramp circuit 428. Acurrent source 431 providing a current I1 is coupled between VDD and oneswitched terminal of a SPST switch 433 having a control input receivinga control signal CTRL3. The other switched terminal of the switch 433 iscoupled to a ramp node 432 developing the ramp voltage VR2. Another SPSTswitch 434 has one switched terminal coupled to the ramp node 432 andits other switched terminal coupled to another current source 435developing a current I2 to GND. The magnitudes of the currents I1 and I2are configured according to the particular embodiment as furtherdescribed herein. Again, transconductance amplifiers may be used toimplement the current sources 433 and 435 and transistors or the likemay be used to implement the switches.

A ramp capacitor 437 with capacitance CR2 is coupled between the rampnode 432 and GND. The ramp node 432 is provided to the positive input ofa comparator 441, to the negative input of another comparator 443, andto the negative input of the comparator 425. The comparator 441 assertsa control signal C4 and the comparator 443 asserts a control signal C5,both provided to the switching controller 415. The control voltage VC isprovided to a negative terminal of a voltage source 449 developing anoffset voltage VP2, having its positive terminal developing a positivewindow voltage provided to the negative input of the comparator 441. VCis also provided to a positive terminal of another voltage source 451developing an offset voltage VN2, having its negative terminaldeveloping a negative window voltage provided to the positive input ofthe comparator 443. The magnitudes of the voltages VP2 and VN2 areconfigured according to the particular embodiment as further describedherein. A SPST switch 445 has its switched terminals coupled between theramp node 432 and the negative input of the comparator 441, and has acontrol input receiving a control signal CTRL5. Another SPST switch 447has its switched terminals coupled between the ramp node 432 and thepositive input of the comparator 443, and has a control input receivinga control signal CTRL6. The switching controller 415 receives C4 and C5and generates the control signals CTRL3-CTRL6.

The comparator 425 is provided in certain embodiments to compare theramp voltages VR1 and VR2 to develops the control signal C3 provided tothe switching controller 415.

The ramp circuit 450, if provided, is configured in similar the samemanner as the ramp circuit 430 for developing a third ramp voltage VR3in certain embodiments as described herein. As further described herein,VR3 may be used as a timing ramp signal for controlling the duration ofone or both switching states S1 and S3 during the buck-boost regulationmode. In some configurations in which only one additional ramp controlsignal is used, the ramp circuit 450 is not provided. A current source456 providing a current I3 is coupled between VDD and one switchedterminal of a SPST switch 453 having a control input receiving a controlsignal CTRL7. The other switched terminal of the switch 453 is coupledto a ramp node 452 developing the ramp voltage VR3. Another SPST switch454 has one switched terminal coupled to the ramp node 452 and its otherswitched terminal coupled to another current source 455 developing acurrent I4 to GND. The magnitudes of the currents I3 and I4 areconfigured according to the particular embodiment as further describedherein. Again, transconductance amplifiers may be used to implement thecurrent sources 456 and 455 and transistors or the like may be used toimplement the switches.

A ramp capacitor 457 with capacitance CR3 is coupled between the rampnode 452 and GND. The ramp node 452 is provided to the positive input ofa comparator 461 and to the negative input of another comparator 463.The comparator 461 asserts a control signal C6 and the comparator 463asserts a control signal C7, both provided to the switching controller415. The control voltage VC is provided to a negative terminal of avoltage source 469 developing an offset voltage VP3, having its positiveterminal developing a positive window voltage provided to the negativeinput of the comparator 461. VC is also provided to a positive terminalof another voltage source 471 developing an offset voltage VN3, havingits negative terminal developing a negative window voltage provided tothe positive input of the comparator 463. The magnitudes of the voltagesVP3 and VN3 are configured according to the particular embodiment asfurther described herein. A SPST switch 465 has its switched terminalscoupled between the ramp node 452 and the negative input of thecomparator 461, and has a control input receiving a control signalCTRL9. Another SPST switch 467 has its switched terminals coupledbetween the ramp node 452 and the positive input of the comparator 463,and has a control input receiving a control signal CTRL10. The switchingcontroller 415 receives C6 and C7 and generates the control signalsCTRL7-CTRL10.

Another comparator 473 receives VR1 at its positive input (e.g., coupledto ramp node 402 or a buffered version thereof), VR3 at its negativeinput (e.g., coupled to ramp node 452 or a buffered version thereof),and asserts a control signal C8 to the switching controller 415. Thecomparator 473 may be provided to develop a control signal C8 in certainembodiments when it is desired to determine when the voltages of VR1 andVR3 cross each other.

Any one or more of the voltage sources 419, 421, 449, 451, 469 and 471may be configured with a fixed voltage or an adjustable voltage. Asshown, each of these voltage sources 419, 421, 449, 451, 469 and 471includes a control input receiving a corresponding control signal fromthe switching controller 415. In this manner, the switching controller415 asserts or adjusts a control signal to set or adjust the voltagelevel of the corresponding voltage source. As previously described, theVP1 and VN1 voltages developed by the voltage sources 419 and 421,respectively, may be adjusted during operation by the frequencycontroller 406 to control steady state frequency. Also, the VP1 and VN1voltages may be adjusted by an offset from nominal levels as furtherdescribed herein. Also, any one or more of the current sources 431, 435,456 and 455 may be configured with a fixed current or an adjustablecurrent. As shown, each of these current sources 431, 435, 456 and 455includes a control input receiving a corresponding control signal fromthe switching controller 415. In this manner, the switching controller415 asserts or adjusts a control signal to set or adjust the currentlevel of the corresponding current source. Alternatively, any one ormore of these voltage sources and current sources may be configured as afixed source depending upon the particular embodiment or configuration.

It is noted that each of the comparators 411, 413, 425, 441, 443, 461,463 and 473 are provided to detect when the voltage levels between twovoltages cross each other, or when one voltage “reaches” the voltage ofanother, and to provide the corresponding control signals C1-C8indicative thereof. For example, when the ramp voltage VR1 is below thevoltage level of VWP yet ramping up towards VWP, the control signal C1is initially asserted low by the comparator 411. When VR1 “reaches” VWP,the comparator 411 switches state and asserts C1 high indicating to theswitching controller 415 that VR1 has reached the level of VWP so thatthe switching controller 415 makes a corresponding switching decision.As generally understood herein, however, each of the comparators areimplemented using physical comparators with offset voltages withhysteresis and the like, so that each comparator switches when onevoltage has risen above or fallen below the other voltage by a smalloffset or threshold voltage. For example, the comparator 411 asserts C1only when VR1>VWP, the comparator 413 asserts C2 high only when VR1<VWN,and so on.

In one embodiment, regulation mode controller 408 is provided, such aswithin the switching controller 415, that makes decisions concerning theregulation mode based on the relative voltage levels of VIN and VOUT.The mode decision may be based on at least one boundary condition suchas when the voltage level VIN is within a predetermined range of VOUT.In one embodiment, when VIN/VOUT>1.2, then the buck regulation mode isindicated, when VIN/VOUT<0.8, then the boost regulation mode isindicated, and otherwise the buck-boost regulation mode is indicated.Different ratios of VIN versus VOUT may be used.

FIG. 5 is a timing diagram illustrating a desired waveform for VR1according to one embodiment of the present invention. A chart alignedabove the timing diagram shows the regulation mode (upper half of chart)and the corresponding switching states (lower half of chart) andswitching state transitions. VR1 is plotted relative to the controlvoltage VC, which is plotted as a dashed line in the center of timingdiagram. It is understood that VC varies during normal operationdepending upon operating conditions. For purposes of clarity, VC isshown as a steady or non-varying signal for purposes of more clearlyillustrating operation of VR1. VWP and VWN are shown plotted above andbelow VC separated by the window voltage VWIN. Also, upper and lower outwindow voltages are plotted as dashed lines, in which VWPP is above thenominal level of VWP by VWIN, and VWNN is below the nominal level of VWNby VWIN. VWPP and VWNN are used in some embodiments. In otherembodiments, either one or both of VWPP and VWNN are now used.

Operation is initially in the buck regulation mode in which operationtransitions between the S2 and S3 switching states as previouslydescribed. During state S3, VR1 ramps up until a time t1 when it reachesVWP, or VR1>VWP, at which time operation transitions to state S2 so thatVR1 ramps down. During state S2, VR1 ramps down until a time t2 when itreaches VWP, or VR1<VWN, at which time operation normally transitionsback to state S3 during the buck regulation mode. Operation may continuein this manner so long as the condition for buck mode remains true.

When the decision is made to switch to the buck-boost regulation mode,then at time t2, when VR1 falls to VWN, (or VR1<VWN) operation insteadtransitions to the buck-boost regulation mode in which VIN is closer to,yet still greater than, VOUT. The decision to transition to thebuck-boost regulation mode is based on a separate logic determination,such as made by the regulation mode controller 408 based on the relativevoltage levels of VIN and VOUT.

In the buck-boost regulation mode beginning at time t2, operationtransitions to the S0 switching state instead of S3. As previouslydescribed in FIG. 3, during the switching state S0 the transistors Q1and Q3 are turned on while Q2 and Q4 are turned off so that the outputinductor 209 is coupled between VIN and GND. In state S0 during thebuck-boost regulation mode, VR1 ramps up towards VWP at a rateproportional to VIN. When VR1>VWP during state S0 of the buck-boostregulation mode at time t3, operation transitions to the switching stateS1. During the switching state S1 the transistors Q1 and Q4 are on whileQ2 and Q3 are off so that the output inductor 209 is coupled between VINand VOUT. At this point, however, VIN is still greater than VOUT in thebuck-boost regulation mode, so that even though this is a dischargestate when in the boost regulation mode, VR1 instead continues to riseto above the nominal level of VWP.

When VR1 meets a timing condition during the switching state S1 asfurther described herein at time t4, operation transitions to theswitching state S2 (Buck Off) in which Q2 and Q4 are on while Q1 and Q3are off. The voltage across the output inductor 209 reverses (to −VOUT)so that VR1 decreases back towards VWN until VR1 drops below VWN, orVR1<VWN. During the buck-boost regulation mode while VIN>VOUT, VWN isadjusted according to an offset from its nominal level as furtherdescribed herein. When VR1<VWN (adjusted) at time t5, operationtransitions to the switching state S3 (Buck On) in which Q1 and Q4 areon while Q2 and Q3 are off, and VR1 rises again. When VR1 meets anothertiming condition during the switching state S3 as further describedherein at time t6, operation transitions to the switching state S0 andVR1 continues to increase at a greater rate as previously describedbetween times t2 and t3. During the buck-boost regulation mode,operation repeatedly and sequentially transitions through the switchingstates S0-S3, or S0, S1, S2, S3, S0, S1, S2, S3, S0, . . . , and so on.The minimum off time during state S2 is also controlled by adjustment ofthe modulator window voltage VWIN, which may be effectuated by adjustingthe voltages of VP1 and VN1 accordingly.

During the buck-boost regulation mode, if the voltage level of VIN fallsbelow the voltage level of VOUT (or VIN<VOUT), the buck-boost regulationmode continues in a substantially similar manner so long as thecondition for the buck or boost regulation modes remains false. In thiscase, VWN remains at its nominal level whereas VWP is adjusted by anoffset as described further herein. During state S2 (Buck Off) in thebuck-boost regulation mode, Q2 and Q4 are on while Q1 and Q3 are off sothat VR1 ramps down at a rate proportional to VOUT until it reaches VWNat time t7, or VR1<VWN. At time t7, the switching state transitions toS3 (Buck On) in which Q1 and Q4 are on while Q2 and Q3 are off. Normallyduring the buck regulation mode when transitioning from state S2 to S3,VR1 rises since VIN is greater than VOUT. In the buck-boost regulationmode when VIN<VOUT, however, VR1 continues to ramp down instead.

When VR1 meets the timing condition during the switching state S3 attime t8, operation transitions to switching state S0 (Boost On) in whichQ1 and Q3 are turned on while Q2 and Q4 are off so that VR1 ramps uptowards VWP. When VR1>VWP (adjusted) at time t9, operation transitionsto switching state S1 (Boost Off) in which Q1 and Q4 are on while Q2 andQ3 are off so that VR1 ramps down at a rate based on a differencebetween VIN and VOUT. When VR1 meets the timing condition during theswitching state S1 at time t10, operation transitions to switching stateS2 (Buck Off) in which Q2 and Q4 are on and Q1 and Q3 are off so thatVR1 ramps down at a higher rate since proportional to VOUT alone. WhenVR1<VWN at time t11, operation during the buck-boost regulation modewould transition back to the switching state S3 as shown at time t7. Inthis case, however, operation transitions to the boost regulation modesince a decision to enter the boost regulation mode has been made.

The decision to transition between the boost regulation mode and thebuck-boost regulation mode is based on a separate logic determination,such as made by the regulation mode controller 408 based on the relativevoltage levels of VIN and VOUT. At time t11 when the threshold conditionis met for boost regulation mode, operation transitions to the switchingstate S0 (Boost On) rather than to switching state S3. In this case, VR1rises at a rate based on VIN until VR1>VWP at time t12, at which timeoperation transitions to the switching state S1. In the boost regulationmode, operation switches between switching states S0 and S1 according tonormal boost regulation mode as previously described. If the voltagelevel of VIN subsequently rises relative to VOUT crossing the boundarycondition in the opposite direction, then operation transitions back tothe buck-boost regulation mode. Operation transitions back into the buckregulation mode if and when the boundary condition for the buckregulation mode is indicated.

During the buck-boost regulation mode, it is desired to maintainhysteretic current mode performance while maintaining steady statefrequency at a target level. As previously noted, VWIN may be adjustedin an attempt to maintain the steady state frequency level at a targetfrequency level. Also, operation repeatedly transitions between statesS0 to S3 to maintain predictable steady state frequency. Furthermore, itis desired to maintain symmetry of the VR1 signal relative to thecontrol signal VC. In order to maintain such symmetry of the VR1 signal,the switching controller 415 enforces the time duration during theswitching state S1, or TS1 (from time t3 to t4 and from time t9 to t10),to be approximately equal to the time duration during the switchingstate S3, or TS3 (from time t5 to t6 and from time t7 to t8), such thatTS1≈TS3. As described further herein, various methods may be used todetermine the upper and lower switching thresholds to meet the timingconditions noted above during switching states S1 and S3 during thebuck-boost regulation mode to ensure that TS1≈TS3 to control switchingfrequency.

As shown in FIG. 5, the switching sequence S0 to S3 repeats during thebuck-boost regulation mode. The durations of the states S1 and S3 arecontrolled so that TS1≈TS3 as further described below. The steady stateswitching frequency is controlled by controlling the window voltageVWIN, or any other method of controlling the collective duration ofstates S0 to S3, or TS0+TS1+TS2+TS3 to be approximately equal to atarget duration TSW. Offset voltages may be determined to adjust VWP andVWN as further described herein for providing the upper and lowerswitching thresholds. The control logic for determining each of theswitching rules as described herein may be implemented in a digital oranalog domain or a combination of both.

The “nominal” levels of VWP and VWN, or VWP_(NOM) and VWN_(NOM), isdefined as the voltage levels that VWP and VWN would normally haveduring the buck and boost regulation modes including any adjustments forfrequency to adjust FSW back to FSS. The upper switching threshold levelmay be determined by adding an offset VOFSP to VWP_(NOM), in which VOFSPis determined according to the following equation (1):

$\begin{matrix}{{VOFSP} = {\frac{{VOUT} - {VIN}}{VOUT}\left( {{VWP}_{NOM} - {VWN}_{NOM}} \right)}} & (1)\end{matrix}$

The lower switching threshold level may be determined by subtracting anoffset VOFSN from VWN_(NOM), in which VOFSN is determined according tothe following equation (2):

$\begin{matrix}{{VOFSN} = {\frac{{VIN} - {VOUT}}{VIN}\left( {{VWP}_{NOM} - {VWN}_{NOM}} \right)}} & (2)\end{matrix}$

It is noted that VOFSN is subtracted from the nominal level of VWNduring the buck-boost mode only while VIN>VOUT. When VIN=VOUT, VOFSNgoes to zero so that VWN is not adjusted. When VIN<VOUT, the offsetvoltage VOFSN goes negative which might otherwise increase the nominalvoltage level of VWN, but instead is not subtracted from VWN. In thismanner, VWN is only adjusted downwards while VIN>VOUT.

In a similar manner, VOFSP is added to the nominal level of VWP duringthe buck-boost mode while VIN<VOUT. When VIN=VOUT, VOFSP goes to zero sothat VWP is not adjusted. When VIN>VOUT, the offset voltage VOFSP goesnegative which might otherwise decrease the nominal voltage level ofVWP, but instead is not added to VWP. In this manner, VWP is onlyadjusted upwards while VIN<VOUT.

Although not explicitly shown, between the times t6 and t7, the voltageof VIN decreases relative to the voltage of VOUT. While VIN>VOUT, theoffset voltage VOFSP stays at VWP_(NOM). The offset voltage VOFSNdecreases until it goes to zero when VIN=VOUT, so that VWN stays atVWN_(NOM) as VIN decreases below VOUT.

As VIN decreases below VOUT, VOFSP increases so that VWP increases aboveVWP_(NOM). Operation is the same for each of the followingconfigurations unless stated otherwise.

In addition, the upper outer window voltage VWPP is determined by addingVWIN to the nominal level of VWP, and the lower outer window voltageVWNN is determined by subtracting VWIN from the nominal level of VWN.These additional window offsets and voltage levels may or may not beused in each of various embodiments as further described herein.

The control system provides very smooth and seamless transition betweenbuck and boost modes. The modulator 400 of the buck-boost chargercontroller 221 only switches 2 transistors between each mode. DCregulation bottlenecks from the power stage are minimized. Operation hasbeen described for continuous conduction mode (CCM), but the controlsystem further provides natural transitions between CCM and adiscontinuous conduction mode (DCM) (or diode emulation mode). Themodulator 400 naturally controls the minimum on and off times of thetransistors of the power stage. The control system uses hystereticcurrent mode control to facilitate stability and dynamic response. Alinear relationship is maintained between control signal and inductorcurrent for smooth mode transitions. The control system provides thebenefit of controlling the switching frequency through the boundariesbetween the buck, buck-boost and boost regulation modes. The transitionsare smooth and relatively continuous with the added buck-boostregulation mode. The following description of the remaining Figures showand describe different variations and embodiments for achievingcontrolled switching frequency.

The following FIGS. 6-14 are timing diagrams of different configurationsof the modulator of FIG. 4 for generating the desired waveform of theramp voltage VR1 shown in FIG. 5 during the buck, boost and buck-boostregulation modes. VC, VWP and VWN are plotted in each timing diagram insimilar manner with certain variations as further described. VWPP andVWNN are plotted in those timing diagrams in which they are used fordeveloping VR1. In each timing diagram, one or both of the additionalramp signals VR2 and VR3 are plotted, in which VR2 is plotting using abolded solid line and VR3 is plotted using a bolded dashed line.

FIG. 6 is a timing diagram illustrating operation of a firstconfiguration of the modulator 400 for generating the desired waveformof VR1 during the buck, boost and buck-boost regulation modes. Thewaveform of VR1 is substantially identical to that of FIG. 5. In thiscase, the modulator 400 includes both of the ramp circuits 430 and 450to use both of the additional ramp signals VR2 and VR3 during thebuck-boost regulation mode. As with FIG. 5, the chart above the timingdiagram shows the regulation mode and the corresponding switching statesand switching state transitions based on the times t2-t11. Also,operation shown in FIG. 6 is initially in the buck regulation mode inwhich operation transitions between the S2 and S3 switching states. Atthe time t2 when the buck-boost mode is indicated as previouslydescribed, operation transitions to the buck-boost regulation mode inwhich operation transitions between the four switching states S0-S3. Atthe time t11 when the boost mode is indicated, operation transitions tothe boost regulation mode in which operation transitions between the S0and S1 switching states.

In both of the buck and boost regulation modes, the ramp circuits 430and 450 essentially remain in a standby mode to set initial states ofthe ramp voltages VR2 and VR3. The voltage source 449 is configured sothat VP2 establishes the voltage VWPP at the negative terminal of thecomparator 441. The switching controller 415 asserts CTRL3-CTRL6 to openswitches 433, 434 and 447 and to close switch 445. In this manner, VR2is clamped high at the voltage VWPP. Similarly, the voltage source 471is configured so that VN3 establishes the voltage VWNN at the positiveterminal of the comparator 463. The switching controller 415 assertsCTRL7-CTRL10 to open switches 453, 454 and 465 and to close switch 467.In this manner, VR3 is effectively clamped low at the voltage VWNN.

In this case, after switching to the buck-boost regulation mode at timet2, when VR1>VWP in switching state S0 as indicated by the controlsignal C1 asserted by the comparator 411 at time t3, the switchingcontroller 415 transitions to switching state S1 and initiates VR2 toramp down from VWPP as shown at 601. In order to initiate VR2, theswitching controller 415 asserts CTRL5 low to open switch 445 andasserts CTRL4 high to close switch 434. The current source 435 beginsdischarging the capacitor 437 so that VR2 ramps down beginning at timet3. The slope of the down ramp VR2 shown at 601 is based on the currentI2 established by the current source 435. In one embodiment, I2∝VOUT, sothat VR2 ramps down at a rate based on the voltage level of VOUT.

During switching state S1, when VR1>VR2 as indicated by the controlsignal C3 asserted by the comparator 425 at time t4, the switchingcontroller 415 transitions to the switching state S2 and resets VR2 backto VWPP by asserting CTRL5 high to re-close the switch 445 (and tore-open switch 434 to avoid contention between the current source 435and the voltage source 449). In switching state S2, when VR1<VWN(adjusted by offset VOFSN) as indicated by the control signal C2asserted by the comparator 413 at time t5, the switching controller 415transitions to the switching state S3 and initiates VR3 as an up rampfrom VWNN as shown at 603. The switching controller 415 initiates theramp of VR3 by asserting CTRL10 low to open switch 467 and by assertingCTRL7 high to close switch 453, so that the current source 456 chargesthe capacitor 457 with current I3. In one embodiment, I3∝VIN so that theslope of VR3 is based on VIN. When VR1<VR3 as indicated by the controlsignal C8 asserted low by the comparator 473 at time t6, the switchingcontroller 415 transitions to the switching state S0 and resets the VR3ramp back to VWNN by closing switch 467 (and asserting CTRL7 low to openswitch 453). VR1 ramps up during the switching state S0 after time t6 ina similar manner as shown between times t2 and t3.

Operation continues in similar manner as VIN drops below VOUT. WhenVIN<VOUT, VWN goes back to its nominal level VWN_(NOM) and VWP isincreased by the offset amount VOFSP as previously described. Again,when VR1<VWN as indicated by the control signal C2 at time t7, theswitching controller 415 transitions to the switching state S3 and againinitiates the up ramp VR3 from VWNN as shown at 605. When VR1<VR3 asindicated by control signal C8 at time t8, the switching controller 415transitions to the switching state S0 and resets VR3 back to VWNN. Inswitching state S0, VR1 rises and when VR1>VWP (adjusted by VOFSP) asindicated by the control signal C1 at time t9, the switching controller415 transitions to the switching state S1 and initiates the down rampVR2 from VWPP as shown at 607. In this case, since VIN<VOUT, VR1decreases during the switching state S1. The down ramp of VR2 at 607,which is based on VOUT, has a faster slope than VR1, which is based onthe difference between VIN and VOUT, and when VR1>VR2 as indicated bythe control signal C3 at time t10, the switching controller 415transitions to the switching state S2 and resets VR2 back to VWPP. Thenegative slope of VR1 increases since based on VOUT alone during theswitching state S2. If it has been determined that operation shouldtransition from the buck-boost regulation mode to the boost mode, thenin switching state S2, when VR1<VWN as indicated by the control signalC2 at time t11, the switching controller 415 transitions to theswitching state S0 instead of state S3 since the boost regulation modeis indicated.

The configuration of the modulator 400 for generating the desiredwaveform of VR1 as shown in FIG. 6 provides the benefits and advantagesas described herein for transitioning between the buck and boostregulation modes of operation, and for enabling smooth operation duringthe buck-boost regulation mode. In this case, additional upper and lowerouter voltages VWPP and VWNN are used along with two additional rampsignals VR2 and VR3 to facilitate switching state transitions during thebuck-boost regulation mode. In this embodiment, certain circuitsimplifications may be made. For example, since VR2 only ramps downrelative to VWPP, the current source 431 and switch 433 along with thevoltage source 451, the switch 447 and the comparator 443 may beeliminated if desired. Also, since VR3 only ramps up relative to VWNN,the current source 455 and switch 454 along with the voltage source 469,the switch 465 and the comparator 461 may be eliminated if desired.

FIG. 7 is a timing diagram illustrating operation of a secondconfiguration of the modulator 400 for generating the desired waveformof VR1 during the buck, boost and buck-boost regulation modes. Thewaveform of VR1 is substantially identical to that of FIG. 5. As withFIG. 5, the chart above the timing diagram shows the regulation mode andthe corresponding switching states and switching state transitions basedon the times t2-t11. Again, from left to right, the regulation modetransitions from the buck mode to the buck-boost mode and then to theboost mode (assuming that the voltage level of VIN decreases from athreshold level above VOUT to another threshold level below VOUT). Thebuck and boost modes are the same and are not further described. VWN andVWP are offset from their nominal levels during portions of thebuck-boost regulation mode in the same manner.

In this case, VR2 ramps down from the voltage VWPP to VWNN and is resetback to VWPP again. In the ramp circuit 430, the voltage source 449 isconfigured so that VP2 establishes the voltage VWPP at the negativeterminal of the comparator 441, and the voltage source 451 is configuredso that VN2 establishes the voltage VWNN at the positive terminal of thecomparator 443. In both of the buck and boost regulation modes, theswitching controller 415 asserts CTRL5 high to clamp VR2 to VWPP.

Operation is similar in switching state S0 during the buck-boostregulation mode, so that when VR1>VWP as indicated by the control signalC1 at time t3, the switching controller 415 transitions to the switchingstate S1 and initiates the down ramp VR2 from VWPP. In order to initiateVR2, the switching controller 415 asserts CTRL5 low to open switch 445and asserts CTRL4 high to close switch 434. The current source 435begins discharging the capacitor 437 so that VR2 ramps down beginning attime t3. The slope of the down ramp VR2 is based on the current I2established by the current source 435. In one embodiment, I2∝VOUT, sothat VR2 ramps down at a rate based on (or otherwise proportional with)the voltage level of VOUT. Meanwhile, VR1 ramps up towards VR2 duringthe switching state S1.

In switching state S1, when VR1>VR2 as indicated by the control signalC3 at time t4, the switching controller 415 transitions to the switchingstate S2 so that VR1 reverses and ramps down. In this case, however, theswitching controller 415 does not reset VR2 so that it continues to rampdown with VR1 at substantially the same rate. When VR1<VWN in switchingstate S2 as indicated by the control signal C2 at time t5, the switchingcontroller 415 transitions to the switching state S3, and VR1 reversesand ramps up as shown. The switching controller 415 does not, however,reset VR2. Instead, VR2 continues to ramp down to VWNN in switchingstate S3. During the switching state S3, when VR2<VWNN as indicated bythe control signal C5 asserted by the comparator 443 at time t6, VR2 isreset back to VWPP, the switching controller 415 transitions to theswitching state S0, and VR1 ramps up at a faster rate as shown. Theswitching controller 415 resets VR2 by asserting CTRL5 to close theswitch 445 to clamp VR2 back to VWPP.

For this point on in the description, it is understood that when a rampsignal, such as VR2 and VR3, is clamped to a particular voltage level,the applicable switches associated with a charging or dischargingfunction, such as the switches 433 and 434 for the current sources 431and 435 or the switches 453 and 454 for the current sources 456 and 455,may also be opened to avoid contention between the current and voltagesources. For example, when VR2 is clamped back to VWPP at time t6, theswitching controller 415 also opens the switch 434 by asserting CTRL4low.

Operation is substantially similar when VIN<VOUT except that VWP is nowoffset by VOFSP as previously described. The current I2 remainsproportional to VOUT so that the slope of down ramping of VR2 continuesto be based on VOUT. In the switching state S2 for the buck-boostregulation mode when VIN<VOUT, VR1 and VR2 are both ramping down atabout the same rate. When VR1<VWN as indicated by the control signal C2at time t7, the switching controller 415 transitions to the switchingstate S3. During the switching state S3, VR2 continues to ramp down atthe same rate towards VWNN, while VR1 ramps down at a slower rateproportional to the difference between VIN and VOUT. When VR2<VWNN asindicated by the control signal C5 at time t8, the switching controller415 resets VR2 back to VWPP and the switching controller 415 transitionsto the switching state S0. VR1 reverses and ramps up during theswitching state S0 as previously described.

Again, when in switching state S0, when VR1>VWP (adjusted) as indicatedby the control signal C1 at time t9, the switching controller 415transitions to the switching state S1 and initiates VR2 to ramp downfrom VWPP once again. In state S1, VR1 ramps down more slowly than VR2,and when VR1>VR2 as indicated by control signal C3 at time t10, theswitching controller 415 transitions to the switching state S2 and bothVR1 and VR2 ramp down at about the same rate. If it is indicated tochange to the boost regulation mode, then when VR1<VWN as indicated bythe control signal C1 at time t11, the switching controller 415transitions to the switching state S0. Since the boost regulation modeis indicated, the switching controller 415 resets VR2 back to VWPPrather than allowing it to continue ramping to VWNN.

The configuration of the modulator 400 for generating the desiredwaveform of VR1 as shown in FIG. 7 provides the benefits and advantagesas described herein for transitioning between the buck, buck-boost andboost regulation modes of operation, and for enabling smooth operationduring the buck-boost regulation mode. In this case, the circuitry maybe further simplified since the ramp circuit 450 and the comparator 473may be eliminated entirely. Only a single down ramp is used during thebuck-boost regulation mode, in which VR2 ramps down from VWPP to VWNNand then is reset back to VWPP. Furthermore, the current source 431 andthe switch 433 may also be eliminated if desired.

FIG. 8 is a timing diagram illustrating operation of a thirdconfiguration of the modulator 400 for generating the desired waveformof VR1 during the buck, boost and buck-boost regulation modes. Thewaveform of VR1 is substantially identical to that of FIG. 5. As withFIG. 5, the chart above the timing diagram shows the regulation mode andthe corresponding switching states and switching state transitions basedon the times t2-t11. Also, from left to right, the regulation modetransitions from the buck mode to the buck-boost mode and then to theboost mode. The buck and boost modes are the same and are not furtherdescribed. VWN and VWP are offset from their nominal levels duringportions of the buck-boost regulation mode in the same manner.

In this case, VR2 ramps down from the voltage VWPP in a similar manner,but rather than ramping down to VWNN, VR2 is held constant for a shortperiod and then is ramped up back to VWPP. In the ramp circuit 430, thevoltage source 449 is configured so that VP2 establishes the voltageVWPP at the negative terminal of the comparator 441. In both of the buckand boost regulation modes, the switching controller 415 asserts CTRL5high to clamp VR2 to VWPP. The current sources 431 and 435 and theswitches 433 and 434 are used to control switching operation. In oneembodiment, I1=I2∝VOUT.

Operation is similar in switching state S0, so that when VR1>VWP asindicated by the control signal C1 at time t3, the switching controller415 transitions to the switching state S1 and initiates the down rampVR2 from VWPP. The switching controller 415 controls CTRL4 and CTRL5 insimilar manner to initiate ramping. The current source 435 beginsdischarging the capacitor 437 so that VR2 ramps down at a rate based onthe current I2 established by the current source 435. In one embodiment,I2∝VOUT, so that VR2 ramps down based on the voltage level of VOUT.Meanwhile, VR1 ramps up towards VR2 during the switching state S1.

In switching state S1, when VR1>VR2 as indicated by the control signalC3 at time t4, the switching controller 415 transitions to the switchingstate S2 so that VR1 ramps down. In this case, the switching controller415 asserts CTRL4 low at time t4 to open the switch 434 so that VR2 doesnot ramp down but instead is held at the voltage level it reached attime t4. The capacitor 437 holds its charge between times t4 and t5.When VR1<VWN in switching state S2 as indicated by the control signal C2at time t5, the switching controller 415 transitions to the switchingstate S3. The switching controller 415 asserts CTRL3 high at time t5 toclose the switch 433 so that the capacitor 437 is charged by the currentsource 431. VR2 thus ramps up from time t5 at a rate proportional to thecurrent I1, which is proportional to the voltage level of VOUT. Inswitching state S3, when VR2>VWPP as indicated by the control signal C4asserted by the comparator 441 at time t6, the switching controller 415transitions to the switching state S0 and re-clamps VR2 at VWPP byasserting CTRL5 to close the switch 445.

Operation is similar when VIN<VOUT, except that VWP is offset ratherthan VWM. Again, I1=I2∝VOUT. During the switching state S2, VR2 is heldsteady while VR1 ramps down until it falls below VWN. When VR1<VWN asindicated by the control signal C2 at time t7, the switching controller415 transitions to the switching state S3 and asserts CTRL3 high toclose the switch 433 so that the capacitor 437 is charged by current I1so that VR2 ramps up. VR1 continues to ramp down during the switchingstate S3. When VR2>VWPP at time t8, the switching controller 415transitions to the switching state S0, clamps VR2 to VWPP, and VR1 rampsup. When VR1>VWP (adjusted) at time t9, the switching controller 415transitions to the switching state S1 and reinitiates VR2 down ramp.During the switching state S1, both VR1 and VR2 ramp down with VR2ramping at a higher rate. When VR1>VR2 at time t10, the switchingcontroller 415 transitions to the switching state S2 and holds VR2steady until time t11. If the boost regulation mode is indicated, thenwhen VR1<VWN at time t11, the switching controller 415 transitions tothe switching state S0 and resets VR2 back to VWPP.

The configuration of the modulator 400 for generating the desiredwaveform of VR1 as shown in FIG. 8 provides the benefits and advantagesas described herein for transitioning between the buck, buck-boost andboost regulation modes of operation, and for enabling smooth operationduring the buck-boost regulation mode. In this case, the modulator 400includes only the ramp circuit 430 for the ramp signal VR2 during thebuck-boost regulation mode, in which the ramp circuit 450 and comparator473 are not used and may be eliminated. Also, the circuitry associatedwith generating and comparing the lower voltage level VWNN may beeliminated. Thus, for example, the voltage source 451, the switch 447and the comparator 443 may also be eliminated.

FIG. 9 is a timing diagram illustrating operation of a fourthconfiguration of the modulator 400 for generating the desired waveformof VR1 during the buck, boost and buck-boost regulation modes. Thewaveform of VR1 is substantially identical to that of FIG. 5. As withFIG. 5, the chart above the timing diagram shows the regulation mode andthe corresponding switching states and switching state transitions basedon the times t2-t11. Again, from left to right, the regulation modetransitions from the buck mode to the buck-boost mode and then to theboost mode. The buck and boost modes are the same and are not furtherdescribed. VWN and VWP are offset from their nominal levels duringportions of the buck-boost regulation mode in the same manner.

In this case, the upper and lower voltages VWPP and VWNN are eliminated.Instead, VR2 ramps up from the voltage level VWN and VR3 ramps down fromVWP. In the ramp circuit 430, the voltage source 449, the comparator441, the current source 435 and the switches 434 and 445 are not used ornot provided. In one embodiment, the voltage source 451 may beconfigured so that VN2 establishes the voltage VWN at the positiveterminal of the comparator 443. In another embodiment, a buffer circuitor the like (not shown) may be used to buffer the voltage VWN of thevoltage source 421 to provide a buffered version of the voltage VWN atthe positive input of the comparator 443. The switching controller 415asserts CTRL6 high during the buck and boost regulation modes to clampVR2 at the voltage VWN.

The ramp circuit 450 may be configured in similar manner, except fordown ramp operation. Here, the voltage source 471, the comparator 463,the current source 456 and the switches 453 and 467 may be eliminated asunnecessary for operation. In one embodiment, the voltage source 469 maybe configured so that VP3 establishes the voltage VWP at the negativeterminal of the comparator 461. In another embodiment, a buffer circuitor the like (not shown) may be used to buffer the voltage VWP of thevoltage source 419 to provide a buffered version of the voltage VWP atthe negative input of the comparator 461. The switching controller 415asserts CTRL9 high during the buck and boost regulation modes to clampVR3 at the voltage VWP.

The current sources 431 and 455 are configured to generate the currentsI1 and I4, respectively, for desired operation for the embodiment ofFIG. 9 to develop the slopes of VR2 and VR3, respectively. The currentI1 is configured according to the following expression (3):

VIN+ABS(VIN−VOUT)+MAX(VIN−VOUT,0)  (3)

in which ABS is the absolute value function, and MAX is the maximum oneof the values in parenthesis. This relationship, along with thecapacitance CR2, establishes the desired slope of VR2 when ramping upfrom VWN. The current I4 is configured according to the followingexpression (4):

−(VOUT+ABS(VIN−VOUT)+MAX(VOUT−VIN,0))  (4)

This relationship, along with the capacitance CR3, establishes thedesired slope of VR3 when ramping down from VWP. In the configurationshown in FIG. 9, VR2 ramps up at a rate based on the expression (3) andVR3 ramps down at a rate based on the expression (4).

At time t2 while in state S0 when the buck-boost regulation mode hasbeen indicated, VR1 ramps up from VWN at a slope proportional to VIN aspreviously described. When VR1>VWP as indicated by the control signal C1at time t3, the switching controller 415 transitions to the switchingstate S1 and asserts CTRL6 low and CTRL3 high to initiate ramping of VR2up from VWN. Both VR1 and VR2 ramp up during the switching state S1, inwhich VR2 ramps up at a higher rate. When VR2>VR1 as indicated by thecontrol signal C3 at time t4, the switching controller 415 transitionsto the switching state S2 and resets VR2 back to VWN such as by openingswitch 433 and closing switch 447. When VR1<VWM as indicated by thecontrol signal C2 at time t5, the switching controller 415 transitionsto the switching state S3 and asserts CTRL9 low and CTRL8 high toinitiate ramping of VR3 down from VWP. During the switching state S3,VR1 ramps up while VR3 ramps down at the rates previously described.When VR3<VR1 as indicated by the control signal C8 at time t6, theswitching controller 415 transitions to the switching state S0 andasserts CTRL9 high and CTRL8 low to reset VR3 back to VWP.

The switching rules are similar when VIN<VOUT. In state S2, VR3 isclamped at VWP and VR1 ramps down. When VR1<VWN as indicated by thecontrol signal C2 at time t7, the switching controller 415 transitionsto the switching state S3 and initiates VR3 to ramp down from VWP. Instate S3, when VR1>VR3 as indicated by the control signal C8 at time t8,the switching controller 415 transitions to the switching state S0 andresets VR3 back to VWP. In the switching state S0, when VR1>VWP asindicated by the control signal C1 at time t9, the switching controller415 transitions to the switching state S1 and initiates VR2 to ramp upfrom VWN. When VR2>VR1 as indicated by the control signal C3 at timet10, the switching controller 415 transitions to the switching state S2and resets VR2 back to VWN. In state S2, when the boost regulation modeis indicated and VR1<VWN at time t11, operation transitions to state S0of the boost regulation mode.

The configuration of the modulator 400 for generating the desiredwaveform of VR1 as shown in FIG. 9 provides the benefits and advantagesas described herein for transitioning between the buck, buck-boost andboost regulation modes of operation, and for enabling smooth operationduring the buck-boost regulation mode. In this case, the outer voltagesVWNN and VWPP are eliminated which may reduce circuitry and simplifyoperation. In this case, the modulator 400 includes portions of both ofthe ramp circuits 430 and 450 to use both of the additional ramp signalsVR2 and VR3 during the buck-boost regulation mode. Since VR2 is onlyramped up from VWN, the circuitry associated with the current source 435and the voltage source 449 may be eliminated if desired. Also, since VR3is only ramped down from VWP, the circuitry associated with the currentsource 456 and the voltage source 471 may be eliminated if desired. Inaddition, VR2 is ramped up by current I1 according to the expression(3), and that VR3 is ramped down by current I4 according to theexpression (4).

FIG. 10 is a timing diagram illustrating operation of a fifthconfiguration of the modulator 400 for generating the desired waveformof VR1 during the buck, boost and buck-boost regulation modes. Thewaveform of VR1 is substantially identical to that of FIG. 5. As withFIG. 5, the chart above the timing diagram shows the regulation mode andthe corresponding switching states and switching state transitions basedon the times t2-t11. Again, from left to right, the regulation modetransitions from the buck mode to the buck-boost mode and then to theboost mode. The buck and boost modes are the same and are not furtherdescribed. VWN and VWP are offset from their nominal levels duringportions of the buck-boost regulation mode in the same manner.

In this case, VR2 is used for both up and down ramps. In one embodiment,the voltage source 449 (VP2) is configured to assert VWP and the voltagesource 451 (VN2) is configured to assert VWN. Alternatively, bufferamplifiers or the like (not show) may be used to buffer the voltage VWPto the negative input of the comparator 441 and to buffer the voltage ofVWN to the positive input of the comparator 443. The current source 431developing I1 is configured according to the expression (3) so that VR2ramps up when the capacitor 437 is charged based on the expression (3).The current source 435 providing I2 is configured according to theexpression (4) so that VR2 ramps down when the capacitor 437 isdischarged based on the expression (4). The switching controller 415asserts the control signals CTRL3-CTRL6 to control operation of VR2 ineach of the switching states S0-S3 during the buck-boost regulationmode.

In the switching state S0 of the buck-boost regulation mode whenVIN>VOUT, VR2 is clamped at VWN while VR1 ramps up towards VWP. WhenVR1>VWP (control signal C1) at time t3, the switching controller 415transitions to the switching state S1 and controls CTRL3 and CTRL6 toinitiate up ramping of VR2. When VR2>VR1 (control signal C3) at time t4,the switching controller 415 transitions to the switching state S2 andclamps VR2 at VWP (including asserting CTRL5 high to close switch 445).When VR1<VWN (control signal C2) at time t5, the switching controller415 transitions to the switching state S3 and initiates down ramping ofVR2 from VWP. When VR1>VR2 (control signal C3) at time t6, the switchingcontroller 415 transitions to the switching state S0 and clamps VR2 atVWN.

In the buck-boost regulation mode when VIN<VOUT, switching operation issubstantially similar. When VR1<VWN at time t7 while in switching stateS2, the switching controller 415 transitions to the switching state S3and initiates down ramping of VR2 from VWP. When VR1>VR2 at time t8while in switching state S3, the switching controller 415 transitions tothe switching state S0 and clamps VR2 low at VWN. When VR1>VWP at timet9 while in switching state S0, the switching controller 415 transitionsto the switching state S1 and initiates up ramping of VR2 from VWN. WhenVR1<VR2 at time t10 while in switching state S1, the switchingcontroller 415 transitions to the switching state S2 and clamps VR2 highat VWP. When VR1<VWN and the boost regulation mode is indicated at timet11, the switching controller 415 transitions to state S0 of the boostregulation mode.

The configuration of the modulator 400 for generating the desiredwaveform of VR1 as shown in FIG. 10 provides the benefits and advantagesas described herein for transitioning between the buck, buck-boost andboost regulation modes of operation, and for enabling smooth operationduring the buck-boost regulation mode. In this case, the modulator 400includes only the ramp circuit 430 for the ramp signal VR2 during thebuck-boost regulation mode, in which the ramp circuit 450 and thecomparator 473 may be eliminated. The outer voltages VWPP and VWNN arealso eliminated. VR2 is ramped up and down by the currents I1 and I2according to the expressions (3) and (4), respectively.

FIG. 11 is a timing diagram illustrating operation of a sixthconfiguration of the modulator 400 for generating the desired waveformof VR1 during the buck, boost and buck-boost regulation modes. Thewaveform of VR1 is substantially identical to that of FIG. 5. As withFIG. 5, the chart above the timing diagram shows the regulation mode andthe corresponding switching states and switching state transitions basedon the times t2-t11. Again, from left to right, the regulation modetransitions from the buck mode to the buck-boost mode and then to theboost mode. The buck and boost modes are the same and are not furtherdescribed. VWN and VWP are offset from their nominal levels duringportions of the buck-boost regulation mode in the same manner.

In this case, a single ramp VR2 is used as an up ramp that ramps up fromthe nominal voltage level of VWN, and ramp VR3 is not used. The voltagesources 419 and 421 are configured in the same manner previouslydescribed for configuring VP1 and VN1 as the voltages VWP and VWN,respectively, in which VWN is offset lower during the buck-boostregulation mode when VIN>VOUT while VWP is at its nominal level, and VWPis offset higher during the buck-boost regulation mode when VIN<VOUTwhile VWP is at its nominal level. The voltage source 449 is configuredso that VP2 maintains the nominal level of VWP at the negative input ofthe comparator 441 throughout the buck-boost regulation mode. Also, thevoltage source 451 is configured so that VN2 maintains the nominal levelof VWN at the positive input of the comparator 443 throughout thebuck-boost regulation mode. Furthermore, VR2 only ramps up from thenominal level of VWN to the nominal level of VWP, so that the currentsource 435 and the switch 434 are not provided or otherwise are notused. Also, the comparator 425 is not provided or not used.

The current source 431 is configured to develop I1 proportional to themaximum one of VIN and VOUT, or I1∝MAX(VIN, VOUT). Thus, when VIN>VOUT,VR2 ramps up at a rate proportional to VIN, and when VIN<VOUT, VR2 rampsup at a rate proportional to VOUT. The switching controller 415 monitorsthe control signals C1, C2, and C4 and asserts applicable ones of thecontrol signals CTRL1-CTRL6 to control operation for each of theswitching states S0-S3 in a similar manner as previously described.

In state S0 during the buck-boost regulation mode while VIN>VOUT, whenVR1>VWP (control signal C1) at time t3, operation transitions to stateS1 and VR2 ramps up from the nominal level of VWN at a rate proportionalto VIN. In state S1, when VR2>VWP_(NOM) at time t4 (control signal C4),operation transitions to state S2 and VR2 is reset back to VWN_(NOM). Instate S2, when VR1<VWN (adjusted) at time t5 (control signal C2),operation transitions to state S3 and VR2 ramps up again from thenominal level of VWN at a rate proportional to VIN. In state S3, whenVR2>VWP_(NOM) at time t6 (control signal C4), operation transitions tostate S0 and VR2 is reset back to VWN_(NOM).

When VIN<VOUT during the buck-boost regulation mode, when VR1<VWN attime t7 (control signal C2) in the switching state S2, operationtransitions to switching state S3 and VR2 ramps up from the nominallevel of VWN at a rate proportional to VOUT (since VOUT>VIN). WhenVR2>VWP_(NOM) at time t8 (control signal C4), operation transitions tostate S0 and VR2 is reset back to VWN_(NOM). In state S0, when VR1>VWP(adjusted) at time t9 (control signal C1), operation transitions tostate S1 and VR2 ramps up from VWN_(NOM) at a rate proportional to VOUT.In state S1, when VR2>VWP_(NOM) at time t10 (control signal C4),operation transitions to state S2 and VR2 is reset back to VWN. In stateS2, when VR1<VWN at time t11 while the boost regulation mode isindicated, operation transitions to the boost regulation mode.

The configuration of the modulator 400 for generating the desiredwaveform of VR1 as shown in FIG. 11 provides the benefits and advantagesas described herein for transitioning between the buck, buck-boost andboost regulation modes of operation, and for enabling smooth operationduring the buck-boost regulation mode. In this case, the modulator 400includes only the ramp circuit 430 to develop the ramp signal VR2 duringthe buck-boost regulation mode, in which the ramp circuit 450 and thecomparator 473 are not used and may be eliminated. VR2 only ramps up andthen is reset back to VWN, so that the current source 435 and switch 434may be eliminated. Also, the comparator 425 may be eliminated.Furthermore, the configuration of the current source 433 developing thecurrent I1 is simplified with a simpler computation as compared to thecurrent computations of the embodiments of FIGS. 9 and 10.

FIG. 12 is a timing diagram illustrating operation of a seventhconfiguration of the modulator 400 for generating the desired waveformof VR1 during the buck, boost and buck-boost regulation modes. Thewaveform of VR1 is substantially identical to that of FIG. 5. As withFIG. 5, the chart above the timing diagram shows the regulation mode andthe corresponding switching states and switching state transitions basedon the times t2-t11. Again, from left to right, the regulation modetransitions from the buck mode to the buck-boost mode and then to theboost mode. The buck and boost modes are the same and are not furtherdescribed. VWN and VWP are offset from their nominal levels duringportions of the buck-boost regulation mode in the same manner.

In this case, the modulator 400 is configured similar to that of theembodiment of FIG. 11, except that the current source 435 and the switch434 are included to develop VR2 as a down ramp. The current source 435develops 12 in the same manner as I1, in which I1=I2∝MAX(VIN, VOUT).Thus, VR2 ramps up and down at a rate based on the maximum one of VINand VOUT. The switching controller 415 asserts CTRL3 high and CTRL4 lowto ramp VR2 up, and asserts CTRL3 low and CTRL4 high to ramp VR2 down.Also, VR2 is held or clamped at the nominal level of VWP or VWN ratherthan being reset back to VWN. For example, the switching controller 415clamps VR2 at VWP_(NOM) by asserting CTRL5 high, and clamps VR2 atVWN_(NOM) by asserting CTRL6 high.

In state S0 during the buck-boost regulation mode while VIN>VOUT, whenVR1>VWP at time t3, operation transitions to state S1 and VR2 ramps upfrom the nominal level of VWN at a rate proportional to VIN. In stateS1, when VR2>VWP_(NOM) at time t4, operation transitions to state S2 andVR2 is clamped to VWP_(NOM). In state S2, when VR1<VWN (adjusted) attime t5, operation transitions to state S3 and VR2 ramps down fromVWP_(NOM) at a rate proportional to VIN. In state S3, when VR2<VWN_(NOM)at time t6, operation transitions to state S0 and VR2 is clamped atVWN_(NOM).

In state S2 during the buck-boost regulation mode while VIN<VOUT, whenVR1<VWN at time t7, operation transitions to state S3 and VR2 ramps downfrom VWP_(NOM) at a rate proportional to VOUT. In state S3, whenVR2<VWN_(NOM) at time t8, operation transitions to state S0 and VR2 isclamped at VWN_(NOM). In state S0, when VR1>VWP (adjusted) at time t9,operation transitions to state S1 and VR2 ramps up from VWN_(NOM) at arate proportional to VOUT. In state S1 when VR2>VWP_(NOM) at time t10,operation transitions to state S2 and VR2 is clamped at VWP_(NOM). Instate S2, when VR1<VWN and the boost regulation mode is indicated attime t11, operation transitions to the switching state S0 of the boostregulation mode.

The configuration of the modulator 400 for generating the desiredwaveform of VR1 as shown in FIG. 12 provides the benefits and advantagesas described herein for transitioning between the buck, buck-boost andboost regulation modes of operation, and for enabling smooth operationduring the buck-boost regulation mode. In this case, the modulator 400includes only the ramp circuit 430 to develop an up and down ramp signalVR2 during the buck-boost regulation mode, in which the ramp circuit 450and the comparator 473 are not used and may be eliminated. Also, thecomparator 425 may be eliminated. Since VR2 ramps up and down, bothcurrent sources 431 and 435 are used, but each with a simplercomputation as compared to the current computations of the embodimentsof FIGS. 9 and 10.

FIG. 13 is a timing diagram illustrating operation of an eighthconfiguration of the modulator 400 for generating the desired waveformof VR1 during the buck, boost and buck-boost regulation modes. Thewaveform of VR1 is substantially identical to that of FIG. 5. As withFIG. 5, the chart above the timing diagram shows the regulation mode andthe corresponding switching states and switching state transitions basedon the times t2-t11. Again, from left to right, the regulation modetransitions from the buck mode to the buck-boost mode and then to theboost mode. The buck and boost modes are the same and are not furtherdescribed. In this case, VWN and VWP are not offset from their nominallevels during the buck-boost regulation mode. Instead, VR3 is used todevelop offset signals VWND and VWPD relative to the nominal levels ofVWN and VWP as further described herein.

The ramp circuit 430 for developing VR2 is configured substantially thesame as that shown and described for the embodiment of FIG. 12, in whichVR2 ramps up and down between the nominal levels of VWN and VWP and isclamped to VWP_(NOM) during the switching state S2 and is clamped toVWN_(NOM) during the switching state S0 during the buck-boost regulationmode. The voltages VP1 and VN1 of the voltage sources 419 and 421 arealso set to the nominal levels of VWP and VWN, respectively. Thecomparators 411 and 413 are used to develop the control signals C1 andC2 only during the buck and boost regulation modes, but not during thebuck-boost regulation mode. The current sources 431 and 435 fordeveloping the currents I1 and I2 are the same as that of FIG. 12, inwhich I1=I2∝MAX(VIN, VOUT).

In the ramp circuit 450, the voltage sources 469 and 471 developing thevoltages VP3 and VN3 may also be set to the nominal voltage levels ofVWP and VWN, respectively. In an alternative embodiment, bufferamplifiers or the like (not shown) may be used to set the voltage at thenegative input of the comparator 461 at the nominal level of VWP, and toset the voltage at the positive input of the comparator 463 at thenominal level of VWN. In either case, the switching controller 415 mayclamp VR3 to the nominal level of VWP by closing switch 465, or mayclamp VR3 to the nominal level of VWN by closing switch 467.

During the buck-boost regulation mode when VIN>VOUT, VR3 is clamped toVWN_(NOM) during the switching state S0, and then is ramped down at arate based on the difference between VIN and VOUT during state S1. Thus,the current source 456 develops I3∝VOUT and the current source 455develops I4∝VIN, and the switching controller 415 asserts CTRL7 andCTRL8 high to close both switches 453 and 454 to ramp VR3 accordingly.During the switching state S2, the switches of the ramp circuit 450 areopened so that VR3 holds steady at a voltage level VWND until theswitching state S3, when VR3 is re-clamped to VWN_(NOM).

During the buck-boost regulation mode when VIN<VOUT, VR3 is insteadclamped to VWP_(NOM) during the switching state S2, and then is rampedup at a rate based on the difference between VIN and VOUT during stateS3. Since the current source 453 develops I3∝VOUT and the current source455 develops I4∝VIN, VR3 ramps up when the switching controller 415asserts CTRL7 and CTRL8 high to close both switches 453 and 454. Duringthe switching state S0, the switches of the ramp circuit 450 are openedso that VR3 holds steady at a voltage level VWPD until the switchingstate S1, when VR3 is re-clamped to VWP_(NOM).

During the buck-boost regulation mode when VIN is about the same asVOUT, or VIN≈VOUT (such as within a small predetermined voltagethreshold), VR3 is clamped at VWN_(NOM) during states S1 and S2 and isclamped at VWP_(NOM) during states S3 and S0. When VIN and VOUT areabout the same, then VWPD is about equal to VWP_(NOM) and VWND is aboutequal to VWN_(NOM). During this condition, the switches 469 and 471 areswitched sufficiently quickly during the S2 to S3 and S0 to S1 switchingstate transitions so that VR3 has time to settle to the nominal level ofeither VWP or VWN. In an alternative embodiment, a separate ramp circuitmay be provided, so that VR3 ramps down from VWN_(NOM) and another rampVR4 (not shown) ramps up from VWP_(NOM).

In state S0 during the buck-boost regulation mode when VIN>VOUT, whenVR1>VWP_(NOM) at time t3 (control signal C1), operation transitions tostate S1 and VR2 ramps up from the nominal level of VWN at a rateproportional to VIN. Also, VR3 ramps down beginning at time t3 from thenominal level of VWN at a rate proportional to VIN−VOUT to develop thevoltage VWND. In state S1, when VR2>VWP at time t4 (control signal S4),operation transitions to state S2 and VR2 is clamped at VWP. Also, thedown ramp action of VR3 is stopped so that VR3 is held constant at VWND.The voltage of VWND relative to the nominal level VWN is variabledepending upon the difference between VIN and VOUT. Thus, rather thanpre-calculate VWND, it is determined by waveform comparison. In stateS2, when VR1<VR3 at VWND at time t5 (control signal C8), operationtransitions to state S3 and VR2 ramps down from VWP_(NOM) at a rateproportional to VIN. Also, VR3 is reset back (or clamped) to the nominallevel of VWN. In state S3, when VR2<VWN_(NOM) at time t6, operationtransitions to state S0 and VR2 is clamped at the nominal level of VWN.

In state S2 during the buck-boost regulation mode when VIN>VOUT, VR3 isclamped at the nominal level of VWP. When VR1<VWN_(NOM) at time t7(control signal C2), operation transitions to switching state S3, VR2 isramped down from VWP_(NOM) at a rate proportional to VOUT, and VR3 isramped up from VWP_(NOM) at a rate based on VOUT−VIN. In state S3, whenVR2<VWN_(NOM) at time t8 (control signal C5), operation transitions tostate S0 and VR3 is held steady, which becomes VWPD for this switchingcycle. Again, VWPD varies based on the nominal level of VWP and thedifference between VIN and VOUT. Also in state S0, VR2 is clamped atVWN_(NOM). In state S0, when VR1>VR3 (at VWPD) at time t9 (controlsignal C8), operation transitions to switching state S1, VR3 is resetback to the nominal level of VWP, and VR2 begins ramping up from thenominal level of VWN at a rate proportional to VIN. In state S1, whenVR2>VWP_(NOM) at time t10 (control signal C4), operation transitions tostate S2 and VR2 is clamped at VWP_(NOM). If conditions indicate changeto boost regulation mode, then at time t11, operation transitions tostate S0 of the boost regulation mode.

The configuration of the modulator 400 for generating the desiredwaveform of VR1 as shown in FIG. 13 provides the benefits and advantagesas described herein for transitioning between the buck, buck-boost andboost regulation modes of operation, and for enabling smooth operationduring the buck-boost regulation mode. In this case, the modulator 400includes the ramp circuit 430 to develop an up and down ramp signal VR2during the buck-boost regulation mode. The complications associated withoffsetting VWN and VWP from their nominal levels is not provided.However, the modulator 400 does include the ramp circuit 450 to generateseparate offset signals VWND and VWPD.

FIG. 14 is a timing diagram illustrating operation of a ninthconfiguration of the modulator 400 for generating the desired waveformof VR1 during the buck, boost and buck-boost regulation modes. Thewaveform of VR1 is substantially similar to that of FIG. 5. As with FIG.5, the chart above the timing diagram shows the regulation mode and thecorresponding switching states and switching state transitions based onthe times t1-t11. Again, from left to right, the regulation modetransitions from the buck mode to the buck-boost mode and then to theboost mode. The buck and boost modes are the same and are not furtherdescribed. VWN and VWP are offset from their nominal levels duringportions of the buck-boost regulation mode in the same manner. In thiscase, VR2 is plotted with a lighter solid line than VR1 for clarity.

In this case, the upper and lower voltages VWPP and VWNN are included oneither side of VWN and VWP. In one embodiment during the buck and boostregulation modes, VR2 is synchronized with the switching of VR1, but isnot used for determination of switching points. Instead, VR2 remainssynchronized to facilitate transition to and from the buck-boostregulation mode. In another embodiment, VR2 remains clamped at eitherVWP or VWN, and begins ramping only when the buck-boost regulation modeis indicated and VR1 intersects either VWP or VWN. As shown in FIG. 14,for example, before a time t1, VR2 is clamped at VWN when the buck-boostregulation mode is indicated. When VR1 next intersects VWN as shown attime t1, VR2 is triggered and begins ramping down towards VWNN. WhenVR2<VWNN, VR2 ramps back up towards VWPP. When VR2>VR1 (or when theyintersect) at time t2, operation transitions to the buck-boostregulation mode. In either embodiment, once VR2 is initiated, it rampsup and down with a triangular waveform between VWPP and VWNN, in whichVR2 ramps up at a rate proportional to VIN, and ramps down at a rateproportional to VOUT.

When VR2>VR1 at time t2 at the transition between the buck andbuck-boost regulation modes, operation transitions to state S0, in whichVR2 ramps up at about the same rate as VR1. When VR1>VWP at time t3,operation transitions to the switching state S1. VR2, however, continuesto ramp up to VWPP, and when VR2>VWPP, VR2 switches and begins rampingdown during the switching state S1. When VR1>VR2 at time t4 (controlsignal C3), operation transitions to state S2. In state S2, when VR1<VWN(adjusted) at time t5 (control signal C2), operation transitions tostate S3 in which VR1 begins ramping back up. VR2, however, continues toramp down to VWNN, and when VR2<VWNN, VR2 switches and begins ramping upduring the switching state S3. When VR2>VR1 at time t6, operationtransitions to state S0.

Operation during the buck-boost regulation mode while VIN<VOUT issimilar. In state S2, when VR1<VWN at time t7, operation transitions tostate S3 while VR2 continues to ramp down to VWNN. When VR2<VWNN, VR2switches and begins ramping up. In state S3, when VR2>VR1 at time t8,operation transitions to the switching state S0. In state S0, whenVR1>VWP (adjusted) at time t9, operation transitions to switching stateS1 while VR2 continues to ramp up towards VWPP. When VR2>VWPP, VR2switches and begins ramping down. In state S1, when VR2<VR1 at time t10,operation transitions to switching state S2. Operation transitions tostate S3 at time t11 in similar manner. At this point, the buck-boostregulation mode may be indicated, in which VWP is reset back to itsnominal voltage level. At time t12 when VR2>VR1, operation transitionsto switching state S0 of the boost regulation mode. VR2 may continueramping synchronous with VR1, or may instead remain clamped at VWN orVWP until the buck-boost regulation mode is once again indicated.

The configuration of the modulator 400 for generating the desiredwaveform of VR1 as shown in FIG. 14 provides the benefits and advantagesas described herein for transitioning between the buck, buck-boost andboost regulation modes of operation, and for enabling smooth operationduring the buck-boost regulation mode. In this case, the modulator 400includes only the ramp circuit 430 for the ramp signal VR2 during thebuck-boost regulation mode, in which the ramp circuit 450 is not usedand may be eliminated. VR2 does ramp between the outer voltages VWPP andVWNN, but the configurations for the currents I1 and I2 are relativelysimple since only based on VIN or VOUT.

The benefits, features, and advantages of the present invention are nowbetter understood with regard to the foregoing description andaccompanying drawings. The foregoing description was presented to enableone of ordinary skill in the art to make and use the present inventionas provided within the context of a particular application and itsrequirements. Various modifications to the preferred embodiment will,however, be apparent to one skilled in the art, and the generalprinciples defined herein may be applied to other embodiments. Forexample, several different configurations are described for themodulator 400 in which circuitry may be eliminated when not used.However, the modulator 400 may simply be implemented with the circuitryillustrated in which only those portions used for a selectedconfiguration are activated. The present invention is not intended to belimited to the particular embodiments shown and described herein, but isto be accorded the widest scope consistent with the principles and novelfeatures herein disclosed. Although the present invention has beendescribed in considerable detail with reference to certain preferredversions thereof, other versions and variations are possible andcontemplated. Those skilled in the art should appreciate that they canreadily use the disclosed conception and specific embodiments as a basisfor designing or modifying other structures for providing the samepurposes of the present invention without departing from the spirit andscope of the invention as defined by the following claim(s).

1. An electronic device, comprising: a hysteretic current modebuck-boost voltage regulator, comprising: a buck-boost voltage converterfor converting an input voltage to an output voltage as controlled by aswitching controller that toggles said buck-boost voltage converterbetween first and second switching states in a boost regulation mode andthat toggles said buck-boost voltage converter between third and fourthswitching states in a buck regulation mode; a primary window circuitcomprising a first voltage source that develops a first upper voltageabove a regulation control voltage, a second voltage source thatdevelops a first lower voltage below said regulation control voltage,wherein a difference between said first upper and first lower voltagesforms a window voltage; a primary ramp circuit that provides a primaryramp voltage relative to said regulation control voltage, wherein saidprimary ramp voltage ramps up at a rate proportional to said inputvoltage in said first switching state, ramps down at a rate proportionalto said output voltage in said third switching state, and rampsproportional to a difference between said input and output voltages insaid second and fourth switching states; wherein during said buck-boostregulation mode, said switching controller transitions from said firstswitching state to said second switching state when said primary rampvoltage reaches said first upper voltage, transitions from said secondswitching state to said third switching state in response to a firsttiming indication, transitions from said third switching state to saidfourth switching state when said primary ramp voltage reaches said firstlower voltage, and transitions from said fourth switching state to saidfirst switching state in response to a second timing indication; and atiming circuit that provides said first and second timing indications tosaid switching controller to ensure that said second and fourthswitching states have approximately the same duration.
 2. The electronicdevice of claim 1, wherein: said first voltage source increases saidfirst upper voltage by a positive offset voltage above a nominal levelof said first upper voltage based on a difference between said input andoutput voltages and a nominal level of said window voltage when saidinput voltage is less than said output voltage; wherein said secondvoltage source decreases said first lower voltage by a negative offsetvoltage below a nominal level of said first lower voltage based on adifference between said input and output voltages and said nominal levelof said window voltage when said input voltage is greater than saidoutput voltage; and wherein said timing circuit comprises: a thirdvoltage source that develops a second upper voltage above said nominallevel of said first upper voltage by said nominal level of said windowvoltage; a fourth voltage source that develops a second lower voltagebelow said nominal level of said first lower voltage by said nominallevel of said window voltage; a second ramp circuit that provides asecond ramp voltage during said buck-boost regulation mode, wherein saidsecond ramp voltage ramps down from said second upper voltage at a rateproportional to said output voltage beginning when transitioning to saidsecond switching state and then resets back to said second upper voltageupon reaching said second lower voltage; a first comparator thatprovides said first timing indication when said second ramp voltagereaches said primary ramp voltage; and a second comparator that providessaid second timing indication when said second ramp voltage reaches saidsecond lower voltage.
 3. The electronic device of claim 1, wherein: saidfirst voltage source increases said first upper voltage by a positiveoffset voltage above a nominal level of said first upper voltage basedon a difference between said input and output voltages and a nominallevel of said window voltage when said input voltage is less than saidoutput voltage; wherein said second voltage source decreases said firstlower voltage by a negative offset voltage below a nominal level of saidfirst lower voltage based on a difference between said input and outputvoltages and said nominal level of said window voltage when said inputvoltage is greater than said output voltage; and wherein said timingcircuit comprises: a third voltage source that develops a second uppervoltage above said nominal level of said first upper voltage by saidnominal level of said window voltage; a second ramp circuit thatprovides a second ramp voltage during said buck-boost regulation mode,wherein said second ramp voltage ramps down from said second uppervoltage at a rate proportional to said output voltage beginning whentransitioning to said second switching state until said first timingindication is provided, wherein said second ramp voltage is held at asteady voltage in response to said first timing indication, and whereinsaid second ramp voltage ramps up at a rate proportional to said outputvoltage in response to transitioning to said fourth switching state; afirst comparator that provides said first timing indication when saidsecond ramp voltage reaches said primary ramp voltage; and a secondcomparator that provides said second timing indication when said secondramp voltage reaches said second upper voltage.
 4. The electronic deviceof claim 1, wherein: said first voltage source increases said firstupper voltage by a positive offset voltage above a nominal level of saidfirst upper voltage based on a difference between said input and outputvoltages and a nominal level of said window voltage when said inputvoltage is less than said output voltage; wherein said second voltagesource decreases said first lower voltage by a negative offset voltagebelow a nominal level of said first lower voltage based on a differencebetween said input and output voltages and said nominal level of saidwindow voltage when said input voltage is greater than said outputvoltage; and wherein said timing circuit comprises: a second rampcircuit that provides a second ramp voltage during said buck-boostregulation mode, wherein said second ramp voltage ramps up from saidfirst lower voltage at a rate proportional to said input voltage plus anabsolute value of a difference between said input and output voltagesplus a maximum one of zero and a difference between said input andoutput voltages beginning when transitioning to said second switchingstate until said first timing indication is provided, and then goes tosaid first upper voltage, wherein said second ramp voltage ramps downfrom said first upper voltage at a rate proportional to said outputvoltage plus an absolute value of a difference between said input andoutput voltages plus a maximum one of zero and a difference between saidinput and output voltages in response to transitioning to said fourthswitching state until said second timing indication is provided, andthen goes to said first lower voltage; a first comparator that providessaid first timing indication when said second ramp voltage reaches saidprimary ramp voltage while said second ramp voltage is ramping up; and asecond comparator that provides said second timing indication when saidsecond ramp voltage reaches said primary ramp voltage while said secondramp voltage is ramping down.
 5. The electronic device of claim 1,wherein: said first voltage source increases said first upper voltage bya positive offset voltage above a nominal level of said first uppervoltage based on a difference between said input and output voltages anda nominal level of said window voltage when said input voltage is lessthan said output voltage; wherein said second voltage source decreasessaid first lower voltage by a negative offset voltage below a nominallevel of said first lower voltage based on a difference between saidinput and output voltages and said nominal level of said window voltagewhen said input voltage is greater than said output voltage; and whereinsaid timing circuit comprises: a third voltage source that provides saidnominal level of said first upper voltage and a fourth voltage sourcethat provides said nominal level of said first lower voltage; a secondramp circuit that provides a second ramp voltage during said buck-boostregulation mode, wherein said second ramp voltage ramps up from saidnominal level of said first lower voltage at a rate proportional to amaximum one of said input and output voltages beginning whentransitioning to said second switching state until said first timingindication is provided, wherein said second ramp voltage ramps up at arate proportional to a maximum one of said input and output voltages inresponse to transitioning to said fourth switching state, and whereinsaid second ramp voltage is reset back to said first lower voltage inresponse to each of said first and second timing indications; a firstcomparator that provides said first timing indication when said secondramp voltage reaches said nominal level of said first upper voltageduring said second switching state; and a second comparator thatprovides said second timing indication when said second ramp voltagereaches said nominal level of said first upper voltage during saidfourth switching state.
 6. The electronic device of claim 1, wherein:said first voltage source increases said first upper voltage by apositive offset voltage above a nominal level of said first uppervoltage based on a difference between said input and output voltages anda nominal level of said window voltage when said input voltage is lessthan said output voltage; wherein said second voltage source decreasessaid first lower voltage by a negative offset voltage below a nominallevel of said first lower voltage based on a difference between saidinput and output voltages and said nominal level of said window voltagewhen said input voltage is greater than said output voltage; and whereinsaid timing circuit comprises: a third voltage source that provides saidnominal level of said first upper voltage and a fourth voltage sourcethat provides said nominal level of said first lower voltage; a secondramp circuit that provides a second ramp voltage during said buck-boostregulation mode, wherein said second ramp voltage ramps up from saidnominal level of said first lower voltage at a rate proportional to amaximum one of said input and output voltages beginning whentransitioning to said second switching state until said first timingindication is provided, wherein said second ramp voltage ramps down at arate proportional to a maximum one of said input and output voltages inresponse to transitioning to said fourth switching state until saidsecond timing indication is provided, wherein said second ramp voltageremains at said nominal level of said first upper voltage in response tosaid first timing indication, and wherein said second ramp voltageremains at said nominal level of said first lower voltage in response tosaid second timing indication; a first comparator that provides saidfirst timing indication when said second ramp voltage reaches saidnominal level of said first upper voltage; and a second comparator thatprovides said second timing indication when said second ramp voltagereaches said nominal level of said first lower voltage.
 7. Theelectronic device of claim 1, wherein: said first voltage sourceincreases said first upper voltage by a positive offset voltage above anominal level of said first upper voltage based on a difference betweensaid input and output voltages and a nominal level of said windowvoltage when said input voltage is less than said output voltage;wherein said second voltage source decreases said first lower voltage bya negative offset voltage below a nominal level of said first lowervoltage based on a difference between said input and output voltages andsaid nominal level of said window voltage when said input voltage isgreater than said output voltage; and wherein said timing circuitcomprises: a third voltage source that develops a second upper voltageabove said nominal level of said first upper voltage by said nominallevel of said window voltage; a fourth voltage source that develops asecond lower voltage below said nominal level of said first lowervoltage by said nominal level of said window voltage; a second rampcircuit that provides a second ramp voltage during said buck-boostregulation mode, wherein said second ramp voltage repeatedly ramps upfrom said second lower voltage to said second upper level at a rateproportional to said input voltage and ramps down from said second upperlevel to said second lower level at a rate proportional to said outputvoltage; a first comparator that provides said first timing indicationwhen said second ramp voltage reaches said primary ramp voltage whenramping down from said second upper level; and a second comparator thatprovides said second timing indication when said second ramp voltagereaches said primary ramp voltage when ramping up from said second lowerlevel.
 8. The electronic device of claim 1, wherein: said first voltagesource increases said first upper voltage by a positive offset voltageabove a nominal level of said first upper voltage based on a differencebetween said input and output voltages and a nominal level of saidwindow voltage when said input voltage is less than said output voltage;wherein said second voltage source decreases said first lower voltage bya negative offset voltage below a nominal level of said first lowervoltage based on a difference between said input and output voltages andsaid nominal level of said window voltage when said input voltage isgreater than said output voltage; and wherein said timing circuitcomprises: a third voltage source that develops a second upper voltageabove said nominal level of said first upper voltage by said nominallevel of said window voltage; a fourth voltage source that develops asecond lower voltage below said nominal level of said first lowervoltage by said nominal level of said window voltage; a second rampcircuit that provides a second ramp voltage during said buck-boostregulation mode, wherein said second ramp voltage ramps down from saidsecond upper voltage at a rate proportional to said output voltagebeginning when transitioning to said second switching state, and thenresets back to said second upper voltage in response to said firsttiming indication; a third ramp circuit that provides a third rampvoltage during said buck-boost regulation mode, wherein said third rampvoltage ramps up from said second lower voltage at a rate proportionalto said input voltage beginning when transitioning to said fourthswitching state, and then resets back to said second lower voltage inresponse to said second timing indication; a first comparator thatprovides said first timing indication when said second ramp voltagereaches said primary ramp voltage; and a second comparator that providessaid second timing indication when said third ramp voltage reaches saidprimary ramp voltage.
 9. The electronic device of claim 1, wherein: saidfirst voltage source increases said first upper voltage by a positiveoffset voltage above a nominal level of said first upper voltage basedon a difference between said input and output voltages and a nominallevel of said window voltage when said input voltage is less than saidoutput voltage; wherein said second voltage source decreases said firstlower voltage by a negative offset voltage below a nominal level of saidfirst lower voltage based on a difference between said input and outputvoltages and said nominal level of said window voltage when said inputvoltage is greater than said output voltage; and wherein said timingcircuit comprises: a second ramp circuit that provides a second rampvoltage during said buck-boost regulation mode, wherein said second rampvoltage ramps up from said first lower voltage at a rate proportional tosaid input voltage plus an absolute value of a difference between saidinput and output voltages plus a maximum one of zero and a differencebetween said input and output voltages beginning when transitioning tosaid second switching state, and then resets back to said first lowervoltage in response to said first timing indication; a third rampcircuit that provides a third ramp voltage during said buck-boostregulation mode, wherein said third ramp voltage ramps down from saidfirst upper voltage at a rate proportional to said output voltage plusan absolute value of a difference between said input and output voltagesplus a maximum one of zero and a difference between said input andoutput voltages beginning when transitioning to said fourth switchingstate until said second timing indication is provided, and then resetsback to said first upper voltage; a first comparator that provides saidfirst timing indication when said second ramp voltage reaches saidprimary ramp voltage; and a second comparator that provides said secondtiming indication when said third ramp voltage reaches said primary rampvoltage.
 10. The electronic device of claim 1, further comprising: asecond ramp circuit that provides a third ramp voltage during saidbuck-boost regulation mode, wherein while said input voltage is greaterthan said output voltage, said third ramp voltage ramps down from saidfirst lower voltage at a rate proportional to said difference betweensaid input and output voltages beginning when transitioning to saidsecond switching state until said first timing indication is provided atwhich time said third ramp voltage is at a second lower voltage, whereinsaid third ramp voltage then remains at said second lower voltage untiltransitioning to said fourth switching state, and wherein while saidinput voltage is less than said output voltage, said third ramp voltageramps up from said first upper voltage at a rate proportional to saiddifference between said input and output voltages beginning whentransitioning to said fourth switching state until said second timingindication is provided at which time said third ramp voltage is at asecond upper voltage, wherein said third ramp voltage then remains atsaid second upper voltage until transitioning to said second switchingstate; wherein during said buck-boost regulation mode while said inputvoltage is greater than said output voltage, said switching controllerinstead transitions from said third switching state to said fourthswitching state when said primary ramp voltage reaches said second rampvoltage, and during said buck-boost regulation mode while said inputvoltage is less than said output voltage, said switching controllerinstead transitions from said first switching state to said secondswitching state when said primary ramp voltage reaches said second rampvoltage; and wherein said timing circuit comprises: a third ramp circuitthat provides a third ramp voltage during said buck-boost regulationmode, wherein said third ramp voltage ramps up from said first lowervoltage at a rate proportional to a maximum one of said input and outputvoltages beginning when transitioning to said second switching stateuntil said first timing indication is provided, wherein said third rampvoltage ramps down from said first upper voltage at a rate proportionalto a maximum one of said input and output voltages in response totransitioning to said fourth switching state until said second timingindication is provided; a first comparator that provides said firsttiming indication when said third ramp voltage reaches said first uppervoltage during said second switching state; and a second comparator thatprovides said second timing indication when said primary ramp voltagereaches said first lower voltage during said third switching state. 11.The electronic device of claim 1, wherein: said buck-boost voltageconverter comprises a first switch coupled between an input voltage anda first end of an output inductor, a second switch coupled between saidfirst end of said output inductor and a reference node, a third switchcoupled between an output voltage and a second end of said outputinductor, and a fourth switch coupled between said second end of saidoutput inductor and said reference node; and wherein said switchingcontroller turns on said first and third switches and turns off saidsecond and fourth switches in said first switching state, turns on saidfirst and fourth switches and turns off said second and third switchesin said second and fourth switching states, and turns on said second andfourth switches and turns off said first and third switches in saidthird switching state.
 12. The electronic device of claim 1, whereinsaid primary ramp circuit comprises: a ramp capacitor developing saidprimary ramp voltage; a first switched current source that charges saidramp capacitor with a current proportional to said input voltage; asecond switched current source that discharges said ramp capacitor witha current proportional to said output voltage; a first comparator thatcompares said primary ramp voltage with said first upper voltage andthat provides a signal indicative thereof to said switching controller;and a second comparator that compares said primary ramp voltage withsaid first lower voltage and that provides a signal indicative thereofto said switching controller.
 13. The electronic device of claim 1,wherein said timing circuit comprises at least one ramp circuit, eachsaid ramp circuit comprising: a ramp capacitor developing a timing rampvoltage; at least one switched current source that either charges ordischarges said ramp capacitor with a predetermined current; at leastone voltage source that develops an offset voltage relative to saidregulation control voltage; and at least one comparator that comparessaid timing ramp voltage with said offset voltage and that provides aselected one of said first and second timing indications.
 14. Theelectronic device of claim 1, wherein said first and second voltagesources are adjusted to adjust said window voltage in order to controlswitching frequency towards a steady state frequency level.
 15. Theelectronic device of claim 1, wherein said switching controller ensuresthat each of said switching states have a least a predetermined minimumperiod.
 16. The electronic device of claim 1, further comprising a modecontroller that selects one of said buck, boost and buck-boostregulation modes based on relative levels of said input and outputvoltages.
 17. The electronic device of claim 1, further comprising aprocessor and peripheral system including a memory coupled to saidhysteretic current mode buck-boost voltage regulator.
 18. A method ofconverting an input voltage to an output voltage using hystereticcurrent mode control, comprising: toggling a buck-boost voltageconverter between first and second switching states in a boostregulation mode when the input voltage is less than the output voltageand toggling the buck-boost voltage converter between third and fourthswitching states in a buck regulation mode when the input voltage isgreater than the output voltage; providing a window voltage including afirst upper voltage above a regulation control voltage and a first lowervoltage below the regulation control voltage; developing a primary rampsignal that replicates current through an output inductor of thebuck-boost voltage converter, in which the primary ramp voltage ramps upat a rate proportional to the input voltage in the first switchingstate, ramps down at a rate proportional to the output voltage in thethird switching state, and ramps proportional to a difference betweenthe input and output voltages in the second and fourth switching states;during a buck-boost regulation mode when the input voltage is within apredetermined boundary of the output voltage, transitioning from thefirst switching state to the second switching state when the primaryramp voltage reaches the first upper voltage, transitioning from thesecond switching state to the third switching state in response to afirst timing indication, transitioning from the third switching state tothe fourth switching state when the primary ramp voltage reaches thefirst lower voltage, and transitioning from the fourth switching stateto the first switching state in response to a second timing indication;and providing the first and second timing indications to ensure that thesecond and fourth switching states have approximately the same durationduring the buck-boost regulation mode.
 19. The method of claim 18,further comprising: increasing the first upper voltage by a positiveoffset voltage above a nominal level of the first upper voltage based ona difference between the input and output voltages and a nominal levelof the window voltage when the input voltage is greater than the outputvoltage; and decreasing the first lower voltage by a negative offsetvoltage below a nominal level of the first lower voltage based on adifference between the input and output voltages and the nominal levelof the window voltage when the input voltage is greater than the outputvoltage.
 20. The method of claim 18, further comprising adjusting thewindow voltage in order to control switching frequency towards a steadystate frequency level.
 21. The method of claim 18, further comprisingpreventing a period of each of the switching states from falling below apredetermined minimum period.
 22. The method of claim 18, furthercomprising selecting between the buck, boost and buck-boost regulationmodes based on relative levels of said input and output voltages. 23.The method of claim 18, wherein said providing the first and secondtiming indications comprises: providing a second upper voltage above anominal level of the first upper voltage by a nominal level of thewindow voltage; providing a second lower voltage below a nominal levelof the first lower voltage by the nominal level of the window voltage;providing a second ramp voltage during the buck-boost regulation modethat ramps down from the second upper voltage at a rate proportional tothe output voltage beginning when transitioning to the second switchingstate and then resetting the second ramp voltage back to the secondupper voltage upon reaching the second lower voltage; providing thefirst timing indication when the second ramp voltage reaches the primaryramp voltage; and providing the second timing indication when the secondramp voltage reaches the second lower voltage.
 24. The method of claim18, wherein said providing the first and second timing indicationscomprises: providing a second upper voltage above a nominal level of thefirst upper voltage by a nominal level of the window voltage; providinga second ramp voltage during the buck-boost regulation mode that rampsdown from the second upper voltage at a rate proportional to the outputvoltage beginning when transitioning to the second switching state untilthe first timing indication is provided, then holding the second rampvoltage at a steady voltage in response to the first timing indication,and then ramping the second ramp voltage up at a rate proportional tothe output voltage in response to transitioning to the fourth switchingstate; providing the first timing indication when the second rampvoltage reaches the primary ramp voltage; and providing the secondtiming indication when the second ramp voltage reaches the second uppervoltage.
 25. The method of claim 18, wherein said providing the firstand second timing indications comprises: providing a second ramp voltageduring the buck-boost regulation mode that ramps up from the first lowervoltage at a rate proportional to the input voltage plus an absolutevalue of a difference between the input and output voltages plus amaximum one of zero and a difference between the input and outputvoltages beginning when transitioning to the second switching stateuntil the first timing indication is provided, and then that goes to thefirst upper voltage, and that ramps down from the first upper voltage ata rate proportional to the output voltage plus an absolute value of adifference between the input and output voltages plus a maximum one ofzero and a difference between the input and output voltages in responseto transitioning to the fourth switching state until the second timingindication is provided, and then that goes to the first lower voltage;providing the first timing indication when the second ramp voltagereaches the primary ramp voltage while the second ramp voltage isramping up; and providing the second timing indication when the secondramp voltage reaches the primary ramp voltage while the second rampvoltage is ramping down.
 26. The method of claim 18, wherein saidproviding the first and second timing indications comprises: providingthe nominal levels of the first upper and lower voltages; providing asecond ramp voltage during the buck-boost regulation mode that ramps upfrom the nominal level of the first lower voltage at a rate proportionalto a maximum one of the input and output voltages beginning whentransitioning to the second switching state until the first timingindication is provided, that ramps up at a rate proportional to amaximum one of the input and output voltages in response totransitioning to the fourth switching state, and resetting the secondramp voltage back to the first lower voltage in response to each of thefirst and second timing indications; providing the first timingindication when the second ramp voltage reaches the nominal level of thefirst upper voltage during the second switching state; and providing thesecond timing indication when the second ramp voltage reaches thenominal level of the first upper voltage during the fourth switchingstate.
 27. The method of claim 18, wherein said providing the first andsecond timing indications comprises: providing the nominal levels of thefirst upper and lower voltages; providing a second ramp voltage duringthe buck-boost regulation mode that ramps up from the nominal level ofthe first lower voltage at a rate proportional to a maximum one of theinput and output voltages beginning when transitioning to the secondswitching state until the first timing indication is provided, thatramps down at a rate proportional to a maximum one of the input andoutput voltages in response to transitioning to the fourth switchingstate until the second timing indication is provided, keeping the secondramp voltage at the nominal level of the first upper voltage in responseto the first timing indication, and keeping the second ramp voltage atthe nominal level of said first lower voltage in response to the secondtiming indication; providing the first timing indication when the secondramp voltage reaches the nominal level of the first upper voltage; andproviding the second timing indication when the second ramp voltagereaches the nominal level of said the lower voltage.
 28. The method ofclaim 18, wherein said providing the first and second timing indicationscomprises: providing a second upper voltage above a nominal level of thefirst upper voltage by a nominal level of the window voltage; providinga second lower voltage below a nominal level of the first lower voltageby the nominal level of the window voltage; providing a second rampvoltage during the buck-boost regulation mode that repeatedly ramps upfrom the second lower voltage to the second upper level at a rateproportional to the input voltage and ramps down from the second upperlevel to the second lower level at a rate proportional to the outputvoltage; providing the first timing indication when the second rampvoltage reaches the primary ramp voltage when ramping down from thesecond upper level; and providing the second timing indication when thesecond ramp voltage reaches the primary ramp voltage when ramping upfrom the second lower level.
 29. The method of claim 18, wherein saidproviding the first and second timing indications comprises: providing asecond upper voltage above a nominal level of the first upper voltage bya nominal level of the window voltage; providing a second lower voltagebelow a nominal level of the first lower voltage by the nominal level ofthe window voltage; providing a second ramp voltage during thebuck-boost regulation mode that ramps down from the second upper voltageat a rate proportional to the output voltage beginning whentransitioning to the second switching state, and that resets back to thesecond upper voltage in response to the first timing indication;providing a third ramp voltage during the buck-boost regulation modethat ramps up from the second lower voltage at a rate proportional tothe input voltage beginning when transitioning to the fourth switchingstate, and that resets back to the second lower voltage in response tothe second timing indication; providing the first timing indication whenthe second ramp voltage reaches the primary ramp voltage; and providingthe second timing indication when the third ramp voltage reaches theprimary ramp voltage.
 30. The method of claim 18, wherein said providingthe first and second timing indications comprises: providing a secondramp voltage during the buck-boost regulation mode that ramps up fromthe first lower voltage at a rate proportional to the input voltage plusan absolute value of a difference between the input and output voltagesplus a maximum one of zero and a difference between the input and outputvoltages beginning when transitioning to the second switching state, andthen that resets back to the first lower voltage in response to thefirst timing indication; providing a third ramp voltage during thebuck-boost regulation mode that ramps down from the first upper voltageat a rate proportional to the output voltage plus an absolute value of adifference between the input and output voltages plus a maximum one ofzero and a difference between the input and output voltages beginningwhen transitioning to the fourth switching state until the second timingindication is provided, and then that resets back to the first uppervoltage; providing the first timing indication when the second rampvoltage reaches the primary ramp voltage; and providing the secondtiming indication when the third ramp voltage reaches the primary rampvoltage.